"Units" on a peptide vial almost always means insulin-syringe units. On a standard U-100 syringe, 1 unit = 0.01 mL — so a unit is really a volume, not an amount of drug. That is why you cannot turn units into mg (or mg into units) without knowing how concentrated your vial is.
Why units↔mg needs a concentration
A unit tells you how much liquid you draw. How much peptide sits in that liquid depends on your reconstitution: vial strength (mg) divided by the bacteriostatic water you added (mL) gives the concentration in mg/mL. Only then does a unit map to a mass.
The formula is:
- Units → mg: mg = units × 0.01 mL × concentration (mg/mL)
- mg → units: units = mg ÷ concentration (mg/mL) ÷ 0.01 mL
Enter your vial and water amounts in the calculator above and it shows the full cascade: concentration, then "X units = Y mL = Z mcg/mg" — which is exactly the units↔mg relationship.
Worked examples
Each answer depends on your concentration, so the example concentration is stated every time.
- 12.5 units to mg: 12.5 × 0.01 = 0.125 mL. At 10 mg/mL that is 1.25 mg; at 5 mg/mL it is 0.625 mg.
- 7.5 units to mg: 0.075 mL. At 10 mg/mL that is 0.75 mg (750 mcg).
- 37.5 units to mg: 0.375 mL. At 10 mg/mL that is 3.75 mg.
- 5 mg to units: at 10 mg/mL, 5 mg = 0.5 mL = 50 units; at 5 mg/mL, 5 mg = 1 mL = 100 units.
- 1.5 mg to units: at 10 mg/mL, 1.5 mg = 0.15 mL = 15 units.
- 200 mcg to units: 200 mcg = 0.2 mg. At 10 mg/mL that is 0.02 mL = 2 units; at 2 mg/mL it is 0.1 mL = 10 units.
- 125 mcg to units: 0.125 mg. At 10 mg/mL that is 0.0125 mL = 1.25 units.
Example reference table
These use two clearly stated example concentrations. Your own vial will differ — use the calculator with your real numbers.
| Units (mL) | At 5 mg/mL | At 10 mg/mL |
|---|---|---|
| 10 units (0.10 mL) | 0.5 mg (500 mcg) | 1.0 mg (1,000 mcg) |
| 20 units (0.20 mL) | 1.0 mg (1,000 mcg) | 2.0 mg (2,000 mcg) |
| 50 units (0.50 mL) | 2.5 mg (2,500 mcg) | 5.0 mg (5,000 mcg) |
Get the concentration first
The concentration comes from how you reconstitute the vial. Work it out with the peptide reconstitution calculator, see where units land on a syringe with the insulin syringe units chart, and convert between mass units with the mg / mcg / IU converter.