mg to units calculator
Updated 24 October 2026
Milligrams measure how much drug you take. The units on an insulin syringe measure volume: on a U-100 syringe, 1 unit is 0.01 mL. To get from one to the other you need a third number, the concentration of your vial in mg per mL. Without it, no calculator can convert mg to units.
Calculator
Draw 25 units (0.25 mL)
2.5 mg at 10 mg/mL on a U-100, 1 mL (100 units) syringe. Round to the nearest mark your syringe has.
Draw to 25 units
U-100, 1 mL (100 units) insulin syringe
Free, no account needed. Your vials stay on this device.
The formula
units = dose (mg) ÷ concentration (mg/mL) × 100
- 2.5 mg at 10 mg/mL: 2.5 ÷ 10 = 0.25 mL = 25 units
- 0.5 mg at 2.5 mg/mL: 0.5 ÷ 2.5 = 0.2 mL = 20 units
- 0.25 mg at 5 mg/mL: 0.25 ÷ 5 = 0.05 mL = 5 units
If your dose is in mcg, divide by 1,000 first: 250 mcg is 0.25 mg. If your label gives the whole vial ("10 mg/2 mL"), divide that too: 10 ÷ 2 = 5 mg/mL.
mg to units chart
| Dose | 1 mg/mL | 2.5 mg/mL | 5 mg/mL | 10 mg/mL |
|---|---|---|---|---|
| 0.25 mg | 25 units (0.25 mL) | 10 units (0.1 mL) | 5 units (0.05 mL) | 2.5 units (0.025 mL) |
| 0.5 mg | 50 units (0.5 mL) | 20 units (0.2 mL) | 10 units (0.1 mL) | 5 units (0.05 mL) |
| 1 mg | 100 units (1 mL) | 40 units (0.4 mL) | 20 units (0.2 mL) | 10 units (0.1 mL) |
| 2.5 mg | over 1 mL | 100 units (1 mL) | 50 units (0.5 mL) | 25 units (0.25 mL) |
| 5 mg | over 1 mL | over 1 mL | 100 units (1 mL) | 50 units (0.5 mL) |
| 10 mg | over 1 mL | over 1 mL | over 1 mL | 100 units (1 mL) |
Why insulin units are different
For insulin, "units" also measure the drug: U-100 insulin has 100 units of insulin in every mL, so the syringe marks and the insulin dose line up. For any other drug, the marks are only a volume scale, and the number of units for a given mg changes with every concentration.
This only works on a U-100 syringe. On a U-40 syringe, 1 unit is 0.025 mL; see units to mL.