How to Read an Insulin Syringe

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.

On a U-100 syringe, 100 units = 1 mL, so 1 unit = 0.01 mL.

Barrel sizes

Barrel	Max units	Typical marks
0.3 mL	30	often 1 or ½ unit
0.5 mL	50	often 1 unit
1 mL	100	often 2 units

Check the marks printed on your own syringe, because they vary by manufacturer.

Reading the plunger

Line up the top (leading) edge of the rubber plunger tip with the line. Read it at eye level.

Illustrative: 15 units = 0.15 mL.

Ask your pharmacist to show you the correct technique for your syringe.

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.

Check your math: Use the free VialMath calculator →

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.