Insulin Units to mL Converter (U-100, U-200, U-500)
Convert an insulin dose in units to mL for U-40, U-100, U-200, U-300 or U-500 insulin, see how many marks to draw, which syringe size fits and how many days a pen or vial lasts.
How it works
volume (mL) = dose (units) ÷ concentration (units/mL) · U-100 syringe marks = mL × 100 · units in container = mL × concentration · days = units in container ÷ ((dose + priming) × injections a day)
Insulin strength is written as U-number = units per mL: U-100 contains 100 units in each mL and is the standard for human use in most countries, while U-40 is common for pets and in some countries, and U-200, U-300 and U-500 are concentrated insulins for people with high requirements. Insulin syringes are graduated in units of U-100 insulin, so drawing any other strength with a U-100 syringe needs a conversion — the cause of serious dosing errors. Concentrated insulins should be given with their own pen or a dedicated U-500 syringe; this converter is for checking volumes, not for improvising. Pens waste a small priming (air-shot) dose before each injection, and opened insulin is usually discarded after 28–56 days whatever is left.
Worked example
A dose of 20 units of U-100 insulin is 20 ÷ 100 = 0.200 mL — 20 marks on a U-100 syringe, which fits a 0.3 mL syringe. A 3 mL pen holds 300 units; at 20 units plus a 2-unit prime once a day (22 units), it lasts 13 days.
Sources: FDA — Humulin R U-500 prescribing information (dedicated U-500 syringe) · Wikipedia — Insulin (medication): concentrations
Frequently asked questions
How many mL is 10 units of insulin?
For U-100 insulin, 10 units is 0.1 mL. For U-40 it is 0.25 mL, for U-200 0.05 mL and for U-500 0.02 mL.
Can I use a U-100 syringe for U-40 insulin?
Only with a conversion, and it is best avoided: each U-40 unit takes 2.5 marks on a U-100 syringe, so 10 units of U-40 insulin is drawn to the 25 mark. Use U-40 syringes with U-40 insulin (common in cats and dogs) whenever possible.
How long does an insulin pen last?
Divide the units in the pen (300 for a 3 mL U-100 pen) by the units used per day including the priming dose. Also check the in-use life on the label — usually 28 days once opened — and discard the pen at that point even if insulin is left.
What is U-500 insulin?
Regular human insulin five times as concentrated as U-100 (500 units/mL) for people who need more than about 200 units a day. It must be given with the U-500 pen or a dedicated U-500 syringe to avoid fivefold errors.
Related calculators
Educational calculation for pharmacists, students and health professionals only — not medical advice or a prescription. Check every result against the product label, an approved compounding reference and local protocols, and have a second person verify any dose before it is given.