Insulin Syringe Unit Calculator
Insulin syringes are marked in units, not milligrams, and a unit means a different volume on a U-100 than on a U-40. This calculator converts your dose into the exact unit marking to draw to, given how your vial was reconstituted.
100 units per mL — pick the syringe you have.
Draw to
BAC water
on a U-100 insulin syringe
Drag the syringe to set your dose, or type the values above.
Enter your vial amount and dose, then type the bacteriostatic water or drag the syringe to see the exact units to draw.
Vial sizes and water volumes are shown for convenience — the dose field is deliberately not prefilled and has no suggestions. Enter your own numbers.
Never do this math twice.
The Pep AI app remembers your vials and doses, shows an interactive syringe you draw to, counts down the doses left in each vial, and reminds you when it's time. Free on iOS and Android.
Why units are not milligrams
A syringe unit is a volume marking, not an amount of compound. Converting between them needs your concentration, which is why the vial and water fields exist:
1. Concentration
Vial amount ÷ water added. A 5 mg vial with 2 mL of water is 2.5 mg/mL.
2. Volume per dose
Your dose ÷ concentration. A 0.5 mg dose at 2.5 mg/mL is 0.2 mL.
3. Units to draw
Volume per dose × 100 for a U-100 syringe (or × 40 for a U-40). 0.2 mL on a U-100 syringe is 20 units.
Worked example
You have a 5 mg vial, you want a 500 mcg dose, and you add 2 mL of bacteriostatic water. Concentration is 5 ÷ 2 = 2.5 mg/mL. Volume per dose is 0.5 ÷ 2.5 = 0.2 mL. On a U-100 syringe that's 0.2 × 100 = 20 units, and the vial holds 10 doses.
The same draw is not the same amount
On a U-100 syringe one unit is 0.01 mL; on a U-40 it is 0.025 mL. Drawing to the 20 mark gives 0.2 mL on one and 0.5 mL on the other — two and a half times as much liquid, and therefore two and a half times as much compound. Any conversion has to know which syringe is in your hand.
Beyond that, how many milligrams sit in one unit depends entirely on your reconstitution. Two people drawing the same number of units from differently mixed vials are drawing very different amounts, which is why a unit figure recorded without the vial's water volume is uninterpretable later.
Read to the flat top edge of the plunger's rubber stopper, not the tip of its cone — see how to read an insulin syringe.
Frequently asked questions
This calculator is provided for informational and educational purposes only and is not medical advice. Always confirm dosing with a qualified healthcare professional and double-check your own measurements before administering anything.
Built by the Pep AI team.