Reading an insulin syringe: units, U-100 and how much to draw
Updated 1 July 2026 · 5 min read
Insulin syringes are marked in 'units', not millilitres, which trips people up. The unit scale depends on the syringe type. This guide explains the relationship so the numbers make sense.
What the U-number means
The U-number is how many units equal one millilitre. A U-100 syringe has 100 units per mL, so 100 units is 1 mL and 50 units is 0.5 mL. A U-40 syringe has 40 units per mL, so the same volume reads as a different number of units.
- U-100: 100 units = 1 mL
- U-50: 50 units = 1 mL
- U-40: 40 units = 1 mL
- U-30: 30 units = 1 mL
From dose to units
To read units, you need the solution's concentration (from reconstitution) and the dose you have chosen. Volume to draw is dose divided by concentration; units are that volume multiplied by the syringe's units-per-mL. The calculator shows a visual syringe so you can see the fill line.
Every calculator result is arithmetic based on your inputs, not a dosing recommendation. Consult a licensed clinician.