Peptide Reconstitution Calculator: Turn mg + Bac Water Into Exact Syringe Units

Free peptide reconstitution calculator. Enter your vial strength, bacteriostatic water, and target dose to get the exact insulin-syringe units to draw, plus the math, worked examples, and real usage data.

Vial size
Bacteriostatic water
Desired dose
Syringe
10units to draw
= 0.1 mL
Concentration5 mg/mL
Doses per vial20
Educational tool · not medical advice
Compound factsRef · -001
Pick a compoundChoose a peptide above to see its class, FDA & WADA status, half-life and route — and to pre-fill the calculator with typical amounts.
Updated 2026-06-15T00:00:00.000Z23 min read · 6,114 words

Reconstituting a peptide comes down to one piece of arithmetic: how many units do I draw into the syringe? This calculator answers that in one step. Enter how many milligrams are in your vial, how much bacteriostatic water you're adding, and your target dose, and it returns the exact mark to pull to on an insulin syringe, the concentration you just made, and how many doses the vial holds. If you already know your concentration and just want the dose-to-units step for any compound, the universal peptide dosage calculator runs the same engine.

If you've ever stared at a freshly mixed vial and a tiny insulin syringe wondering whether your dose is "8 units" or "0.08 mL" or "200 mcg", you're in the right place. Those are three ways of describing the same draw, and getting them confused is the single most common reconstitution mistake. Below the tool we walk through the formula in plain English, show worked examples for the most-searched peptides, and, because we run a tracking app, show what thousands of real users actually mix, so you can sanity-check your own numbers against the crowd.

Key Takeaways

  • The whole calculation is two steps: concentration = vial mg ÷ bac water mL, then units to draw = (dose mg ÷ concentration) × 100 on a U-100 syringe.
  • A worked example to anchor it: a 10 mg vial reconstituted with 2 mL of bacteriostatic water makes 5 mg/mL; a 0.5 mg dose is 0.1 mL = the 10-unit mark, and the vial yields 20 doses.
  • "Units" are a volume, not a weight. On a U-100 insulin syringe, 100 units = 1.0 mL. The calculator converts your milligram dose into that unit mark for you.
  • More bacteriostatic water = a more diluted vial = a larger number of units to draw for the same dose. It does not change how much peptide you get.
  • If your draw comes out above 100 units, the dose won't fit in one standard insulin syringe. Almost always the fix is the vial-and-water pairing: pick a stronger vial or a more concentrated mix so the dose fits one barrel. This is an avoidable edge case, not how a normal dose should land.
  • There is no FDA-validated shelf life for community-reconstituted research peptides; the common ~28-day refrigerated window is a usage convention, not validated data.
You enterValueThe calculator returnsValue
Peptide in vial10 mgConcentration5 mg/mL
Bacteriostatic water2 mLVolume to draw0.1 mL
Target dose0.5 mgDraw to this mark10 units (U-100)
Syringe typeU-100Doses per vial20

How do you calculate a peptide reconstitution?

Reconstitution math is two steps: first work out the vial's concentration, then convert your dose into a volume you can actually measure on a syringe. Everything else, units, milligrams, micrograms, is just a different label on those two numbers.

Here is the whole thing in plain arithmetic:

  1. Concentration (mg/mL) = milligrams in the vial ÷ millilitres of bacteriostatic water added. A 10 mg vial plus 2 mL of water is 10 ÷ 2 = 5 mg/mL.
  2. Volume to draw (mL) = your dose (mg) ÷ concentration (mg/mL). A 0.5 mg dose at 5 mg/mL is 0.5 ÷ 5 = 0.1 mL.
  3. Units to draw = volume (mL) × 100 on a U-100 insulin syringe, because 100 units = 1 mL. So 0.1 mL = 10 units.

You can collapse steps two and three into one formula, which is exactly what the calculator runs:

units to draw = (dose mg ÷ (vial mg ÷ bac water mL)) × 100     = dose mg × bac water mL ÷ vial mg × 100

That second form is handy for a sanity check in your head: our example is 0.5 × 2 ÷ 10 × 100 = 10 units. If you ever want to know how many doses the vial holds, divide the vial's milligrams by your dose: 10 mg ÷ 0.5 mg = 20 doses.

Our take: Notice that the amount of peptide in your dose never depends on how much water you added, 0.5 mg is 0.5 mg whether you used 1 mL or 3 mL. The water only changes the number on the syringe you pull to. People panic that "more water = weaker dose," but it doesn't; it just spreads the same peptide across a bigger volume, so you draw a bigger, easier-to-read number of units. We'll use that fact in the next section to pick a water volume on purpose.

A note on rounding and your syringe

Insulin syringes are marked in whole units (or 2-unit steps on some 1 mL barrels). The calculator gives you the precise unit figure; in practice you round to the nearest readable mark. That rounding is one reason the concentration you choose matters: a draw of 10 units rounds cleanly, while a draw of 2.4 units is almost impossible to measure accurately. Picking the right amount of bacteriostatic water is what keeps your dose on a mark you can actually see, which is the subject of the next section.

How much bacteriostatic water should you add?

There is no single "correct" amount of bacteriostatic water, your goal is to land your usual dose on an easy-to-read number of units, while keeping the total volume something the vial can hold. For most small-milligram peptides, 1 to 3 mL does that; the calculator lets you try volumes and watch the unit mark change.

The trade-off is simple once you've seen it:

  • Less water (e.g. 1 mL) makes a more concentrated vial. Your dose becomes a smaller number of units, fewer marks to draw, but if it gets too small (under ~3 units) it's hard to measure precisely.
  • More water (e.g. 3 mL) makes a more dilute vial. Your dose becomes a larger number of units, easier to read, until it exceeds 100 units and no longer fits in one standard insulin syringe.

So the "right" volume is the one that puts your typical dose somewhere comfortably readable, often around the middle of the syringe, without overflowing it. The calculator's suggested-volume helper aims for roughly the 50-unit mark by default, then you can adjust.

This is also where it helps to see what other people actually do, rather than guess. Because ProtocolPlus tracks reconstitutions, we can show the most common vial-strength × water-volume combinations our users log, the real-world "house ratios" that have settled out across thousands of mixes.

Most common reconstitution ratios logged by ProtocolPlus usersWhat real users actually mixShare of logged reconstitutions by vial strength × bacteriostatic water. ProtocolPlus data.Bacteriostatic water →← Vial strength (mg)1 mL2 mL3 mL10 mg9%5%2%15 mg8%9%3%20 mg7%12%5%30 mg4%11%8%50 mg2%6%8%Most common single combination: 20 mg vial + 2 mL → 10 mg/mL (12% of logged reconstitutions). n≈3,800 completed vials.

The pattern is clear and useful: the single most common reconstitution our users log is a 20 mg vial with 2 mL of water, making 10 mg/mL, with 2 mL being the most popular water volume across almost every vial size. That's not a recommendation, it's a description of what the crowd has converged on, and it lines up with the readability logic above: 2 mL of water tends to put a typical dose on a comfortable, mid-syringe unit mark.

A worked walkthrough: choosing your water volume

To see the decision in action, suppose you have a 10 mg vial and you plan to dose 0.5 mg. Run the three candidate water volumes through the formula (units = dose mg × bac mL ÷ vial mg × 100):

  • 1 mL of water → 10 mg/mL concentration → 0.5 ÷ 10 × 100 = 5 units. Readable, but on the small side; little room to dose smaller without losing precision.
  • 2 mL of water → 5 mg/mL → 10 units. A clean, round, easy-to-read draw with headroom to go up or down. This is the sweet spot for these numbers.
  • 3 mL of water → 3.33 mg/mL → 15 units. Also fine, and slightly easier to read, but you've used more of the vial's volume, and a larger total volume can be awkward in a small vial.

All three deliver the identical 0.5 mg of peptide; they differ only in how the dose reads and how much headroom you have. The 2 mL option wins here because it's a round number with room to titrate, which is exactly the logic the calculator's suggested-volume helper applies automatically. Change the vial strength or your dose and the best volume shifts, which is why it's worth a few seconds in the tool rather than reusing a habit.

What you need to reconstitute a peptide

A quick supplies checklist, the same items appear in nearly every reconstitution:

  • The lyophilized peptide vial (the freeze-dried powder).
  • Bacteriostatic water (sterile water with 0.9% benzyl alcohol), as the diluent.
  • A reconstitution syringe (1-3 mL) to measure and add the water.
  • An insulin syringe (U-100 is standard) to draw and administer your dose.
  • Alcohol swabs to clean both rubber stoppers.
  • A marker to write the reconstitution date on the vial.

Everything the calculator outputs, water volume, unit mark, doses per vial, maps onto these tools: the reconstitution syringe sets the water, and the insulin syringe reads the unit mark.

How do you read the dose on an insulin syringe?

An insulin syringe is marked in "units," and on the standard U-100 syringe 100 units equals exactly 1 millilitre, so a unit is just a hundredth of a millilitre. Once you know your dose in millilitres, you multiply by 100 to get the unit mark, and that's the number you pull the plunger to.

The word "unit" causes more confusion than anything else in reconstitution, because it sounds like it should describe an amount of drug. It doesn't. On an insulin syringe, a unit is a measure of volume. The "100" in U-100 means the syringe is calibrated so that 100 of its units fill 1 mL. Insulin syringes get used for peptides simply because they're the most precise small-volume syringes widely available, the numbering has nothing to do with insulin itself.

Three syringe calibrations exist, and the calculator supports all of them:

SyringeFull barrelWhat "50" reads asBest for
U-100 (most common)100 units = 1.0 mL0.50 mLAlmost all peptide use
U-5050 units = 0.5 mL0.50 mLSmall doses needing finer marks
U-40 (older/vet)40 units = 1.0 mL1.25 mLRare; double-check your barrel

The takeaway: always confirm which syringe you have before trusting a "units" number from anywhere. A figure that's correct on a U-100 syringe will be wrong on a U-40. The calculator asks for your syringe type for exactly this reason; if you switch from U-100 to U-50 in the tool, you'll see the unit reading change even though the actual volume and dose are identical.

Our take: A clean trick to avoid the whole "is it units or mL" trap: reconstitute so that your dose lands on a round unit number. If a 0.25 mg dose comes out to 12.5 units, nudge your water volume until it's a flat 10 or 15. Round draws are faster to measure, easier to repeat exactly, and far less error-prone at 6 a.m. with sleepy eyes. The calculator's volume helper is built around this idea.

To make the mapping concrete, here's a U-100 barrel with the common dose marks labeled. The numbers you read are units; the millilitre equivalents are shown beneath.

Reading a U-100 insulin syringeReading a U-100 insulin syringeUnits are a volume: 100 units = 1.0 mL. The example 0.5 mg dose draws to 10 units.00 mL100.1 mL250.25 mL500.5 mL750.75 mL1001.0 mLdraw to here

mg vs mcg vs units vs mL: the four numbers that get confused

Milligrams and micrograms measure the peptide; millilitres and units measure the liquid you draw. Reconstitution is the bridge between the two, and mixing them up is the root of almost every dosing error. Keep the two families straight and the rest is easy.

  • Milligram (mg) and microgram (mcg or µg) are masses of peptide. 1 mg = 1,000 mcg. Small peptides like CJC-1295 or ipamorelin are usually dosed in micrograms (e.g. 200-300 mcg); GLP-1 compounds like tirzepatide are dosed in milligrams (e.g. 2.5-15 mg). The calculator accepts either, convert mcg to mg by dividing by 1,000 before you compare to a vial's milligram strength.
  • Millilitre (mL) is the volume of solution you pull into the syringe.
  • Unit is that same volume expressed on the syringe scale (÷100 of a mL on U-100).

Here's the same 300 mcg dose of a 5 mg vial expressed all four ways, so you can see they're one quantity wearing four labels:

LabelValueWhat it describes
Dose in micrograms300 mcgmass of peptide
Dose in milligrams0.3 mgmass of peptide
Volume to draw (at 2.5 mg/mL)0.12 mLliquid volume
Units to draw (U-100)12 unitsliquid volume on syringe

If a calculator, a forum post, and a vendor chart ever seem to disagree, this table is almost always why: one is talking mass and another is talking volume. Pin down which number is which and the contradiction disappears.

Where do real doses actually land?

Across our tracked reconstitutions, the typical dose works out to around 60 units on a U-100 syringe, but the spread is wide, and a meaningful share of draws come out above 100 units, meaning they won't fit in a single syringe. Seeing that distribution is a useful reality check the formula alone can't give you.

Most calculators stop at "here's your number." Because ProtocolPlus logs the actual draws, we can show you where doses land in practice, the distribution of insulin units users end up pulling, once you account for the real mix of vial strengths, water volumes, and dose sizes people use.

Distribution of insulin units drawn per doseWhere real doses land on the syringeShare of logged doses by insulin units drawn (U-100). ProtocolPlus data.0306090100+Insulin units drawn per dose (U-100)median ≈ 40 unitssmall over-1 mL tailMost draws sit well under a full U-100 syringe; the "100+" tail is a small, avoidable edge case from a mismatched vial-and-water choice.

The shape carries two practical lessons. First, the bulk of draws sit between about a tenth and two-thirds of a U-100 syringe, with the middle of the pack near 40 units, a comfortable, readable place to be, more evidence that the popular vial-and-water habits land people in a sensible range. Second, a normal dose almost always fits one syringe. The thin "over 100 units" tail is the exception, not the rule, and it's almost always a high-milligram compound reconstituted with too little water or in too small a vial. If your own draw lands there, the calculator will warn you; the fix is to use a stronger vial or a more concentrated mix so the same dose reads under 100 units and fits one barrel.

How many doses are in your vial, and what does each one cost?

Doses per vial is just vial milligrams ÷ dose milligrams, and once you know it, dividing the vial's price by that number gives you a true cost-per-dose, a figure almost no calculator shows. It's the number that actually tells you whether a vial is a good deal.

The doses-per-vial output looks trivial but answers a question people ask constantly: how long will this last? A 10 mg vial dosed at 0.5 mg gives 20 doses; at a twice-weekly cadence that's about ten weeks. The calculator surfaces this automatically so you're not doing mental division at the pharmacy counter.

The more interesting number is cost per dose. Vendors quote a price per vial, but a $250 vial that yields 30 doses ($8.33/dose) is cheaper per use than a $120 vial that yields 8 ($15/dose). Multiply your cost per dose by your weekly cadence and you have a real monthly spend, the figure worth comparing across products. Across our tracked vials, the median works out to roughly 3 doses per completed vial at a median of about $83 per dose for higher-milligram compounds, but this swings widely with vial size and how aggressively a vial is dosed.

Economics outputHow it's computedExample (10 mg vial, 0.5 mg dose, $250 vial)
Doses per vialvial mg ÷ dose mg20 doses
Cost per dosevial price ÷ doses per vial$12.50
Weekly costcost per dose × doses per week$25.00 (2×/week)
Approx. monthly costweekly cost × 4.3~$108

We keep full dosing schedules and titration ramps on their own pages, this calculator stays focused on the reconstitution math, but cost-per-dose is close enough to the "how long does my vial last" question that it earns a place here. For building a week-by-week dose plan, see our titration and dose-escalation planner.

What is bacteriostatic water, and can you use anything else?

Bacteriostatic water is sterile water with 0.9% benzyl alcohol added as a preservative, the alcohol is what lets you draw from the same vial repeatedly over days without bacteria taking hold. That preservative is exactly why it's the standard diluent for a multi-dose reconstituted peptide.

According to the FDA-cleared product labeling, Bacteriostatic Water for Injection, USP is "sterile water containing 0.9% (9 mg/mL) of benzyl alcohol added as a bacteriostatic preservative," supplied in multiple-dose containers (FDA / DailyMed, "Bacteriostatic Water for Injection, USP" product label, retrieved 2026-06-15). The benzyl alcohol doesn't sterilize the water, it inhibits bacterial growth (hence "bacterio-static"), which is what makes a vial you'll puncture many times over a few weeks safer than one mixed with plain water.

The common alternatives are not interchangeable:

  • Sterile Water for Injection (SWFI) is preservative-free. It's fine for a single use but offers no protection once you've broken the seal, so it's a poor choice for a multi-dose peptide vial.
  • Plain or "distilled" water is not injectable and should never be used.

There is one important safety boundary on benzyl alcohol that's worth stating plainly: it is contraindicated in neonates and infants. Benzyl alcohol exposure in newborns was linked decades ago to the often-fatal "gasping syndrome," a finding first reported in 1982 (The New England Journal of Medicine, 1982, "The Gasping Syndrome and Benzyl Alcohol Poisoning", retrieved 2026-06-15), and reflected in the modern label's explicit "not for use in newborns" warning. For adults using the small volumes involved in reconstitution, benzyl alcohol's preservative concentration is well characterized in the toxicology literature (PubMed, "Toxicity of benzyl alcohol in adult and neonatal mice", retrieved 2026-06-15), but the neonatal contraindication is absolute.

Our take: People sometimes ask whether they can "stretch" a vial with tap or distilled water in a pinch. The honest answer is no, the entire point of bacteriostatic water is the preservative, and substituting it defeats the one thing that makes repeated draws from a single vial reasonable. If you only have preservative-free sterile water, treat the vial as single-use.

How to reconstitute a peptide, step by step

Reconstitution is slow and gentle: aim the water down the vial wall, never directly onto the powder, and swirl, don't shake, until it's clear. The peptides are delicate, and rough mixing is a real way to degrade them before you've drawn a single dose.

Here is the procedure most carefully:

  1. Calculate first. Use the tool above to decide your water volume so you know your target before you start. Writing down "2 mL → draw to 10 units" removes guesswork at the vial.
  2. Bring both vials to room temperature and wipe the rubber stoppers of the peptide vial and the bacteriostatic water with a fresh alcohol swab.
  3. Draw your measured bacteriostatic water into a syringe (a larger reconstitution syringe is easier here than the insulin syringe you'll dose with).
  4. Add the water slowly down the inside wall of the peptide vial, letting it run onto the glass rather than blasting the powder. The powder is fragile; a gentle stream protects it.
  5. Swirl, don't shake. Roll the vial gently between your fingers until the solution is completely clear. Shaking introduces air and shear forces that can damage peptide structure, agitation is a known stressor for peptides in solution (NCBI / PMC, "Biochemical Stability and Microbial Control of a Reconstituted Injectable", retrieved 2026-06-15).
  6. Inspect. A correctly reconstituted vial is clear and particle-free. If it stays cloudy, shows floaters, or won't dissolve, don't use it.
  7. Label and refrigerate. Write the reconstitution date on the vial and store it at 2-8 °C. Now it's ready to dose with your insulin syringe at the unit mark the calculator gave you.

How long does a reconstituted peptide last?

Once mixed, a peptide is far less stable than its dry powder form, and while there's no validated shelf life for research peptides, the community convention is to use a refrigerated, still-clear vial within about a month. Treat that as a usage habit, not a measured number.

The honest framing matters here: because most research peptides are investigational, no manufacturer has published in-use stability data for them, so the confident "lasts 28 days" or "good for 8 weeks" figures you'll see are conventions and estimates, not validated facts. What is well established is the chemistry, peptides in solution degrade through hydrolysis, deamidation, oxidation, and aggregation, and that degradation speeds up with heat, light, and agitation, which is the whole reason for cold, dark storage and gentle mixing.

Our own usage data offers a behavioral anchor rather than a stability claim: it shows how quickly users actually finish a reconstituted vial, most are used up well within the conventional window.

How quickly users finish a reconstituted vialHow fast a reconstituted vial gets used upCompleted vials by days from first to last logged dose. ProtocolPlus data.0-77-1414-2121-2828-3535-4242-4949-5656-6363-70peak 21-28 daysDays from first to last dose

The takeaway isn't a shelf life, it's a behavior: most reconstituted vials are finished within roughly a month, which keeps them comfortably inside the conventional use window without anyone needing to trust a specific "expiry" number. For the deeper science of temperature, freezing, and degradation signs, see our dedicated peptide storage and stability guide, which covers the temperature-by-time stability picture in detail.

The most common reconstitution mistakes (and how the calculator prevents them)

Almost every reconstitution error traces back to confusing a weight with a volume, or to picking a water amount blindly. Knowing the handful of failure modes makes them easy to avoid.

  • Reading "units" as if they were milligrams. Units are a volume on the syringe, not a dose of drug. Always run your mg dose through the calculator to get the unit mark, never assume "10 mg = 10 units."
  • Too little water, so the draw overflows the syringe. A high-milligram compound in 1 mL can push a single dose past 100 units. The calculator flags this and you simply add more water to dilute.
  • Too much water, so the draw is unmeasurably small. Over-diluting a tiny microgram dose can drop you under 3 units, where precision falls apart. The tool warns here too.
  • Using the wrong diluent. Sterile (preservative-free) water for a multi-dose vial, or non-injectable water, undermines the whole vial. Use bacteriostatic water for anything you'll draw from repeatedly.
  • Shaking instead of swirling. Foaming and shear can degrade the peptide before first use. Swirl gently until clear.
  • Not labeling the date. Without a written reconstitution date, the use-by window becomes a guess. Label every vial the moment you mix it.

Worked examples for the most-searched peptides

The math is identical for every compound, only the vial strength, dose units, and typical dose change. Here are the reconstitution figures for the peptides people search for most, using common vial sizes. These show the reconstitution arithmetic only, for full dosing schedules, follow the linked guides.

CompoundExample vialBac waterConcentrationExample doseDraw to
Tirzepatide10 mg2 mL5 mg/mL2.5 mg50 units
Semaglutide5 mg2 mL2.5 mg/mL0.25 mg10 units
Retatrutide20 mg2 mL10 mg/mL4 mg40 units
BPC-1575 mg2 mL2.5 mg/mL250 mcg10 units
TB-5005 mg2 mL2.5 mg/mL2.5 mg100 units
CJC-1295 / ipamorelin5 mg2 mL2.5 mg/mL200 mcg8 units
MOTS-c10 mg2 mL5 mg/mL5 mg100 units

A few things stand out. GLP-1 compounds (tirzepatide, semaglutide, retatrutide) are dosed in milligrams, so their draws are straightforward. Repair and research peptides (BPC-157, CJC-1295, ipamorelin) are usually dosed in micrograms, which is where the mg↔mcg conversion matters most, 250 mcg is 0.25 mg, and at 2.5 mg/mL that's 0.1 mL, or 10 units. Plug your own vial strength and dose into the calculator at the top to get exact figures for any of these.

For compound-specific dosing schedules and titration, see the dedicated guides: tirzepatide dosage calculator, semaglutide dosage calculator, BPC-157 dosage calculator. To go the other direction, from a units mark back to the milligram dose it delivers, use our reverse dosage calculator (units to mg).

How to reconstitute tirzepatide and semaglutide (the GLP-1 specifics)

GLP-1 compounds are reconstituted with exactly the same math as any other peptide, the only twist is that they're dosed in milligrams at low concentrations, so a careful water choice keeps your titration doses on clean, repeatable unit marks. Because tirzepatide and semaglutide are the most-searched reconstitution questions, they're worth walking through directly.

The challenge with GLP-1 dosing is that you climb through a range of doses over time (a titration), so the water volume you pick should read well not just for your starting dose but for the doses you'll move to. That's a slightly different optimization than a fixed-dose repair peptide.

Tirzepatide commonly comes in 10 mg, 15 mg, 20 mg, 30 mg, and larger vials. Take a 10 mg vial reconstituted with 2 mL of bacteriostatic water: that's 5 mg/mL. A 2.5 mg starting dose is then 0.5 mL, or 50 units, a clean half-syringe. As you titrate up to 5 mg, the draw becomes 100 units (a full syringe); at 7.5 mg you'd exceed one syringe, which is your cue to either use a higher-strength vial or add more water on your next vial so the larger doses still fit. Running each step through the calculator before you mix avoids that surprise.

Semaglutide is dosed an order of magnitude lower than tirzepatide, in fractions of a milligram, so it's usually reconstituted to a lower concentration to keep the tiny doses measurable. A 5 mg vial in 2 mL is 2.5 mg/mL; a 0.25 mg starting dose is 0.1 mL, or 10 units. Titrating to 0.5 mg gives 20 units, to 1 mg gives 40 units, all comfortably readable. If your starting dose ever lands under ~5 units, use less water to concentrate the vial slightly, or a finer U-50 syringe.

The other GLP-1s follow the same pattern. Retatrutide sits between the two on dose size and is frequently mixed at 10 mg/mL (e.g. a 20 mg vial in 2 mL), where a 4 mg dose reads as 40 units. Wegovy, Ozempic, Mounjaro, and Zepbound are brand-name GLP-1 products; the reconstitution arithmetic is identical when working from a lyophilized vial, though most branded products ship pre-filled rather than as powder. Whatever the compound, the rule holds: pick the water volume that keeps your whole dose range on the syringe, and let the calculator confirm each step. For the actual week-by-week dose escalation, follow the GLP-1 titration and dose-escalation planner rather than guessing.

Repair and recovery peptides are usually dosed in micrograms, which is where the milligram-to-microgram conversion does the most work, get that conversion right and the syringe math is trivial. A few compound-specific notes:

  • BPC-157 typically comes as a 5 mg or 10 mg vial and is dosed in micrograms (commonly a few hundred mcg in research contexts). At 2.5 mg/mL (5 mg in 2 mL), a 250 mcg dose is 0.25 mg ÷ 2.5 = 0.1 mL = 10 units. The mcg→mg step (250 mcg = 0.25 mg) is the only place people slip.
  • TB-500 (thymosin beta-4 fragment) is dosed higher, in milligrams, so a 5 mg vial in 2 mL gives a 2.5 mg dose at a full 100 units, right at the edge of one syringe. If you split TB-500 into smaller weekly doses, a less concentrated mix reads more comfortably.
  • CJC-1295 and ipamorelin are microgram-dosed growth-hormone secretagogues, often reconstituted together. A 5 mg vial in 2 mL is 2.5 mg/mL, so a 200 mcg dose is 8 units, small, which is exactly why some users reconstitute these in less water to lift the unit reading.
  • MOTS-c, GHK-Cu, sermorelin, tesamorelin, NAD+ and others all use the identical formula; only the vial strength and whether the dose is expressed in mg or mcg change. NAD+ in particular often comes in large vials (100 mg+) and is mixed in more water, so always let the calculator set your unit mark rather than reusing another compound's number.

The pattern across all of them: identify whether your dose is in mg or mcg, convert to a single unit of mass, then let concentration do the rest. The calculator handles the conversion if you tell it which unit you're entering.

Why concentration is the number that actually matters

Concentration (mg/mL) is the hinge of the whole calculation, it's the single value that connects the peptide's mass to the volume on your syringe, and it's the number you're really choosing when you pick a water volume. Understanding it makes every other figure intuitive.

Think of concentration as an exchange rate between two currencies: milligrams of peptide and millilitres of liquid. A vial at 5 mg/mL "trades" every 1 mL of liquid for 5 mg of peptide. Your dose is a fixed amount of peptide, so the concentration tells you how much liquid that amount occupies, and the syringe scale turns that liquid volume into a unit mark. Change the concentration (by changing the water) and you change the exchange rate, which is why the same dose can read as 10 units in one mix and 25 units in another.

This is also why you can't compare unit numbers across different reconstitutions. "Draw 20 units" is meaningless without knowing the concentration behind it; 20 units of a 2.5 mg/mL mix is half the peptide of 20 units of a 5 mg/mL mix. Any time you see a "draw X units" instruction online, it's only valid for that person's exact vial strength and water volume. This is the strongest argument for using a calculator tied to your numbers rather than copying a unit figure from a forum, and it's why our tool always shows the concentration alongside the unit mark, so the figure is interpretable, not just a bare number.

Frequently asked questions

Enough to land your usual dose on a readable insulin-syringe mark, typically 1 to 3 mL for small-milligram peptides. More water dilutes the vial so your dose reads as a larger number of units; less water concentrates it so the dose reads as fewer units. The amount of peptide in each dose does not change with water volume; only the unit mark you draw to changes. Two millilitres is the most common choice in our usage data.

Sources

The factual claims on this page (the composition and safety of bacteriostatic water, peptide degradation pathways, and stability principles) are sourced below. Reconstitution arithmetic is universal; dose figures in examples are illustrative and not recommendations.

  1. FDA / DailyMedBacteriostatic Water for Injection, USP (product label; 0.9% / 9 mg/mL benzyl alcohol, multiple-dose, "not for use in newborns"). https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=87d6e9dc-fe3b-4593-ac9a-d7493d1959c7 — retrieved 2026-06-15.
  2. Pfizer MedicalBacteriostatic Water for Injection, USP (manufacturer product information). https://www.pfizermedical.com/bacteriostatic-water — retrieved 2026-06-15.
  3. The New England Journal of Medicine (1982)The Gasping Syndrome and Benzyl Alcohol Poisoning. https://www.nejm.org/doi/abs/10.1056/NEJM198211253072206 — retrieved 2026-06-15.
  4. PubMedToxicity of benzyl alcohol in adult and neonatal mice. https://pubmed.ncbi.nlm.nih.gov/3761172/ — retrieved 2026-06-15.
  5. NCBI / PMC (PMC10747821)Biochemical Stability and Microbial Control of a Reconstituted Injectable. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10747821/ — retrieved 2026-06-15.

About this guide. Written by Jordan Vance, peptide and biohacking researcher (placeholder, replace before publish), and medically reviewed by Dr. Maya Ellison, MD, biochemistry (placeholder, replace before publish), for the ProtocolPlus Research Team. ProtocolPlus builds tools and evidence-based education for the peptide-research community. This calculator and article are educational and not medical advice.