Insulin Syringe Units, Explained
Written and reviewed by Evan Marlow, developer of DosePlot · Updated 2026-08-20
A U-100 insulin syringe divides every milliliter into 100 units — that is the whole system. Units are a volume scale, not an amount of drug: 25 units is always 0.25 mL, but how much compound that contains depends on your solution's concentration.
How do I read a dose on an insulin syringe?
Read at the front edge of the plunger seal— the edge nearest the needle — with the syringe at eye level. The diagram shows a 50-unit (0.5 mL) syringe drawn to 25 units.
Units to mL conversion table (U-100)
| Units | Volume |
|---|---|
| 5 units | 0.05 mL |
| 10 units | 0.10 mL |
| 20 units | 0.20 mL |
| 25 units | 0.25 mL |
| 40 units | 0.40 mL |
| 50 units | 0.50 mL |
| 100 units | 1.00 mL |
Barrels come in 0.3 mL (30 units), 0.5 mL (50 units), 1 mL (100 units). The smaller the barrel, the finer and easier to read the scale — some 0.3 mL and 0.5 mL syringes even mark half units.
The U-40 mismatch: the one real trap
U-100 is not the only concentration scale. U-40 insulin (today mostly veterinary) is 40 units per mL, and its syringes divide each mL into 40 units instead of 100. Draw U-40 insulin to the "same number" on a U-100 syringe and you get 40% of the intended dose; the reverse over-doses by 2.5×.[1]The rule: the syringe scale must match the liquid's labeled concentration — and for reconstituted peptides, where you set the concentration, the syringe only ever measures volume. The mg math lives in your reconstitution ratio.
Working out units for a reconstituted peptide? The calculator converts vial size and water volume straight into units on your syringe.
Open the reconstitution calculatorCommon questions
How many units are in 1 mL on a U-100 syringe?
100. U-100 means the syringe scale is built for insulin concentrated at 100 units per mL, so the unit marks divide each mL into 100 parts: 1 mL = 100 units, 0.5 mL = 50 units, 0.25 mL = 25 units, 0.1 mL = 10 units.
How do I convert units to mL?
On a U-100 syringe, divide units by 100. 40 units = 0.4 mL; 15 units = 0.15 mL. Going the other way, multiply mL by 100: 0.3 mL = 30 units.
Do syringe units measure milligrams?
No. Units measure volume on the syringe (a fraction of a mL), not the amount of compound. How many milligrams are in that volume depends entirely on your solution's concentration in mg/mL - which, for a reconstituted peptide, depends on how much water was added to the vial.
Choosing the syringe itself? See syringe types and sizes.
More in this guide
Part of the complete guide to syringes and needle sizes.
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