Units measure volume, not mass
The lines on an insulin syringe count units of volume. On a U-100 syringe, one unit is 0.01 mL and 100 units is 1 mL. How much of a substance sits in those units depends on the solution's concentration, which you set when you added water to the vial.
mg = units ÷ 100 × concentration (mg/mL)
units = mg ÷ concentration (mg/mL) × 100
Units to mg chart
Amount contained in common unit readings at four concentrations. A 5 mg vial mixed with 2 mL is 2.5 mg/mL.
| Units | 1 mg/mL | 2.5 mg/mL | 5 mg/mL | 10 mg/mL |
|---|---|---|---|---|
| 1 (0.01 mL) | 10 mcg | 25 mcg | 50 mcg | 100 mcg |
| 2 (0.02 mL) | 20 mcg | 50 mcg | 100 mcg | 200 mcg |
| 5 (0.05 mL) | 50 mcg | 125 mcg | 250 mcg | 500 mcg |
| 10 (0.1 mL) | 100 mcg | 250 mcg | 500 mcg | 1 mg |
| 15 (0.15 mL) | 150 mcg | 375 mcg | 750 mcg | 1.5 mg |
| 20 (0.2 mL) | 200 mcg | 500 mcg | 1 mg | 2 mg |
| 25 (0.25 mL) | 250 mcg | 625 mcg | 1.25 mg | 2.5 mg |
| 30 (0.3 mL) | 300 mcg | 750 mcg | 1.5 mg | 3 mg |
| 50 (0.5 mL) | 500 mcg | 1.25 mg | 2.5 mg | 5 mg |
| 100 (1 mL) | 1 mg | 2.5 mg | 5 mg | 10 mg |
How to read your result
The converter above shows the concentration of your mix and how much one unit holds. Keep that number handy: if one unit holds 25 mcg, then 4 units is 100 mcg and 10 units is 250 mcg, with no calculator needed.
For a dose-first workflow, use the peptide dosage calculator. To pick a water volume that makes your doses round numbers, use the BAC water calculator.
Conversion questions
How many mg is 10 units?
It depends on the concentration. Ten units is always 0.1 mL on a U-100 syringe. If the solution is 2.5 mg/mL, 0.1 mL contains 0.25 mg (250 mcg). If it is 5 mg/mL, it contains 0.5 mg. Enter your vial size and water to get the exact figure.
How many units is 1 mg?
Divide 1 mg by the concentration in mg/mL and multiply by 100. At 5 mg/mL, 1 mg is 0.2 mL, or 20 units. At 2.5 mg/mL, it is 40 units.
Is a unit always 0.01 mL?
On a U-100 insulin syringe, yes: 100 units fill 1 mL. Other syringes, such as U-40 syringes used for some veterinary insulins, are marked differently, so this converter only applies to U-100 syringes.
Why is there no fixed conversion between units and mg?
Because units measure volume and milligrams measure mass. The same 10 units can hold very different amounts depending on how much powder was dissolved in how much liquid.