If you already know your concentration, converting a peptide dose to insulin-syringe units — or units back to milligrams — is a one-line calculation, and this tool does it both ways. Enter your concentration in mg/mL and either a mass (mg or mcg) or a unit count, and it returns the other. There's no vial size or water to set up here: this is the focused converter for when the concentration is already known. For the full picture (doses per vial plus the per-compound directory) the universal peptide dosage calculator is the hub above this tool, and if you started from a unit count instead, the reverse units-to-mg calculator runs the conversion the other way. (If you still need to work out your concentration, start with the Reconstitution Calculator.)
Key Takeaways
- The formula: units = (mass mg ÷ concentration mg/mL) × 100 on a U-100 syringe. Reverse it: mg = (units ÷ 100) × concentration.
- Anchor example: at 5 mg/mL, a 0.5 mg amount is 0.1 mL = 10 units; and 10 units is 0.5 mg — the conversion runs both ways.
- "Units" are a volume. On a U-100 syringe, 100 units = 1 mL, so one unit is 0.01 mL. The number depends entirely on your concentration.
- mg or mcg: the converter takes either. 1 mg = 1,000 mcg; at 5 mg/mL, every 50 mcg is one unit.
- Syringe matters: the same volume reads differently on U-100, U-50, and U-40 barrels — the converter supports all three.
- Conversion only. No vial or doses-per-vial here; for those, use the reconstitution or dosage calculators.
| You enter | Value | The converter returns | Value |
|---|---|---|---|
| Direction | mg → units | Volume | 0.1 mL |
| Concentration | 5 mg/mL | Units to draw | 10 units (U-100) |
| Amount | 0.5 mg | (reverse: 10 units) | = 0.5 mg |
How do you convert mg to units (and back)?
Converting either way needs just two numbers: your concentration and the amount you're converting — the vial and water that produced that concentration don't enter into it. Units are volume, and concentration is the exchange rate between mass and volume.
Both directions in plain arithmetic, on a U-100 syringe (100 units = 1 mL):
- Mass → units. Volume (mL) = mass ÷ concentration, then units = volume × 100. A 0.5 mg amount at 5 mg/mL is 0.5 ÷ 5 = 0.1 mL = 10 units.
- Units → mass. Volume (mL) = units ÷ 100, then mass = volume × concentration. 10 units is 0.1 mL, and 0.1 mL × 5 mg/mL = 0.5 mg.
The only thing you must know is the concentration. If you don't, it comes from the vial and water you mixed (concentration = vial mg ÷ bac water mL), which the Reconstitution Calculator works out for you.
Units-per-mg at common concentrations
The handiest shortcut is that at any concentration, 1 mg is worth 100 ÷ concentration units — so the same dose reads as very different unit numbers depending on how concentrated your vial is. The grid below is a quick lookup.
Read the grid two ways. Down a column, a bigger dose is more units at the same concentration. Across a row, a more dilute vial (lower mg/mL) makes the same dose a larger, easier-to-read draw — which is why microgram peptides are often mixed weaker, and concentrated ones like glutathione read small. For anything off the grid, the converter handles it exactly.
Converting micrograms to units
For a microgram-dosed peptide, either convert the dose to milligrams first (1 mg = 1,000 mcg) or work in micrograms throughout — at 2,500 mcg/mL, every 25 mcg is one unit. The converter's mcg toggle does this for you.
Microgram peptides (BPC-157, sermorelin, Selank, Semax, CJC-1295) are where the unit slip bites hardest, because a 1,000× error hides easily among small numbers. Keep the concentration and the amount in the same family: a 250 mcg dose at 2,500 mcg/mL (the same as 2.5 mg/mL) is 250 ÷ 2,500 × 100 = 10 units. If you'd rather think in milligrams, that's 0.25 mg at 2.5 mg/mL — identical answer. The converter accepts whichever you prefer; just match the toggle to your number.
U-100, U-50, and U-40: the same volume, different numbers
Insulin syringes come in three calibrations, and the unit count for a given volume differs on each — so the converter asks which barrel you're using. A unit is always a fraction of a millilitre, but which fraction depends on the syringe.
- U-100 is the standard: 100 units = 1 mL, so 1 unit = 0.01 mL. Most peptide instructions assume it.
- U-50 is a smaller 0.5 mL barrel also marked to 50 units; the spacing between marks is wider, which makes small draws easier to read, but a unit is the same 0.01 mL as U-100.
- U-40 is an older, rarer calibration (often a red-capped veterinary syringe) where 40 units = 1 mL, so each unit is 0.025 mL — 2.5× larger. The same volume reads as a smaller unit number, and mixing it up with U-100 is a real dosing error. Always confirm which barrel you're holding.
Why concentration is the only number that matters here
A converter doesn't care how you reached your concentration — two completely different vials that land at the same mg/mL convert mass to units identically. That's what makes this a pure conversion tool rather than a reconstitution one.
Concentration is the exchange rate between the mass of peptide and the volume of liquid, and once it's fixed, the mg-to-units relationship is fixed with it. A 5 mg vial in 1 mL and a 10 mg vial in 2 mL both give 5 mg/mL, and on both, 0.5 mg is 10 units — the vials are different, but the conversion is the same. This is why the converter asks only for the concentration: the vial size and water volume have already done their job by setting it. It's also the reason a unit count copied from someone else is meaningless without their concentration. If a vendor or forum post says "draw 20 units," that number is only correct on the exact concentration they used; feed your concentration into the converter and you'll get the unit mark that actually matches your dose.
The flip side is just as useful. Because the relationship is a fixed ratio, you can move in either direction with equal confidence: planning a dose (mass to units) and checking a draw you've already made (units to mass) are the same calculation run forward and backward. A 12-unit draw on a 2.5 mg/mL vial is 0.3 mg whether you set out to inject 0.3 mg or you're verifying after the fact.
Common mistakes when converting mg to units
Most conversion errors come from one of three slips: using the wrong unit family, applying a concentration that isn't yours, or assuming the wrong syringe calibration. Each produces a wrong-but-plausible number, which is what makes them easy to miss.
- Mixing milligrams and micrograms. The biggest one. Dividing a microgram dose by a milligram concentration (or vice versa) is off by exactly 1,000. If a 250-something dose comes out as thousands of units, or a fraction of one, a unit mismatch is almost always why. Keep the amount and the concentration in the same family, or use the mcg toggle so the converter aligns them.
- Using a concentration that isn't yours. A unit count is only valid for one concentration. Borrowing "draw 15 units" from a different vial gives you the wrong dose because their mg/mL differs from yours. Always convert from your own concentration.
- Assuming U-100 on a U-40 barrel. A U-40 syringe reads the same volume as a smaller unit number (2.5× larger per unit). If you calculate units for U-100 but draw on a U-40, the dose is off. Confirm the calibration before you read the mark, and set it in the converter.
- Treating units as a dose. Units measure volume, not peptide mass. "I drew 10 units" doesn't tell you the dose until you convert through your concentration — which is exactly what this tool is for.
Because the converter computes from the concentration and amount you actually enter, it removes the copying-and-assuming errors; the unit family and the syringe calibration are the two choices left to you, so they're the ones worth confirming each time.
When to use this converter versus the other tools
Use this converter when your concentration is already known and you just need to swap between mass and units; use a different tool when your starting point is a vial, a dose plan, or a drawn syringe. They share one engine, so the numbers always agree.
- This converter — you know your concentration and want mg ↔ units, fast, both directions.
- Reconstitution Calculator — you have a dry vial and need to work out the concentration (and how much water to add) first.
- Peptide Dosage Calculator — you want the full picture for a dose: units, doses per vial, and the per-compound directory.
- Reverse Calculator (units → mg) — you drew a number of units from a known vial and want the mg or mcg it delivered.
Worked examples, both directions
A few conversions at common concentrations, to sanity-check the tool. Each works the same in reverse.
- 0.25 mg at 2.5 mg/mL = 0.1 mL = 10 units; reverse, 10 units = 0.25 mg.
- 1 mg at 10 mg/mL = 0.1 mL = 10 units; reverse, 10 units = 1 mg.
- 300 mcg at 2,500 mcg/mL (2.5 mg/mL) = 0.12 mL = 12 units; reverse, 12 units = 300 mcg.
- 100 mg at 200 mg/mL = 0.5 mL = 50 units; reverse, 50 units = 100 mg.
Read any of them backward and the converter gives the original number — that's the point of a bidirectional tool: it verifies your draw as readily as it plans it.
Frequently asked questions
Sources
This is a mathematical utility. The conversion follows the standard U-100 insulin-syringe convention (100 units = 1 mL); U-50 and U-40 calibrations are noted where they differ. Units are a volume, not a dose. Peptides covered are research compounds and are not FDA-approved.
- U-100 / U-50 / U-40 insulin syringe standards — U-100: 100 units = 1 mL; U-40: 40 units = 1 mL; the basis of every conversion on this page.
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. This converter and article are educational and not medical advice.