U-40 vs U-100 Syringes

Updated October 2026 · Educational math explainer, not medical advice.

The numbers below are made-up examples to show the arithmetic. They are not dose suggestions. Always use the dose your prescriber gave you and the instructions from your pharmacist.

The number tells you how many units equal 1 mL. U-100 = 100 units per mL, U-40 = 40 units per mL. In the US, 30-, 50- and 100-unit insulin syringes are usually all U-100; the number is how much the syringe holds, not a different scale.

Same volume, different reading (illustrative)

0.25 mL reads as 25 units on U-100 and 10 units on U-40.

If you calculate for one scale and draw on another, the amount will be wrong. Use the syringe your pharmacy gives you, and confirm the scale with your pharmacist.

Related guides: Reading a U-100 syringe, U-100 Syringe Chart.

Not medical advice. VialMath is a math tool. It does not recommend doses. Follow your prescriber/pharmacist and your product labeling. All numbers on this page are illustrative only.

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Try it with your own numbers: open the calculator. It shows every step so you can check the math.

This tool does arithmetic on numbers you enter. It does not recommend doses. Confirm with your prescriber or pharmacist.