Insulin Units to mg Calculator
Converts insulin international units (IU) to milligrams (mg) based on the molecular weight of each insulin type.
How to Use This Calculator
- Enter the insulin dose in international units (IU).
- Select the insulin type — each has a slightly different mg-per-unit factor based on its molecular weight.
- Read the equivalent mass in milligrams, with the calculation shown.
This is a pharmacology/reference conversion. Insulin is always prescribed and given in units — never in milligrams.
Conversion Reference Table
| Insulin | mg per IU | IU per mg | Molecular Weight |
|---|---|---|---|
| Human insulin (Regular / NPH) | 0.0347 mg | ~28.8 IU | 5808 Da |
| Insulin lispro (Humalog) | 0.0348 mg | ~28.7 IU | 5808 Da |
| Insulin aspart (NovoLog) | 0.0349 mg | ~28.7 IU | 5826 Da |
| Insulin glargine (Lantus) | 0.0364 mg | ~27.5 IU | 6063 Da |
| Insulin degludec (Tresiba) | 0.0346 mg | ~28.9 IU | ~6103 Da |
The international unit is defined by biological activity, not mass — values are approximate and vary by reference standard.
Units, Milligrams and Concentration — What's the Difference?
The international unit (IU)
An insulin unit measures biological activity, not weight, set against a WHO reference standard (about 28.85 units per mg of human insulin). Because activity is what lowers glucose, units keep dosing consistent even though analogs differ slightly in molecular weight.
How units, mg and the "U-number" relate
Three things are easy to mix up: units (activity, how you dose), milligrams (mass, used only in research/compounding), and the U-number / concentration (units per mL, e.g. U-100). The converter above links units and mg; for units ↔ mL and concentration, use the insulin conversion calculator.
Don't confuse insulin with GLP-1 medications
Drugs like semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) are dosed in milligrams, but they are not insulin — they're a different class (GLP-1/GIP receptor agonists). Seeing "mg" on those pens doesn't mean insulin is dosed in mg.
Frequently Asked Questions
How many mg is one unit of insulin?
For human insulin, one international unit is about 0.0347 mg, based on the WHO standard of 28.846 IU per mg. Analog insulins differ slightly — for example, glargine is about 0.0364 mg per unit.
Why is insulin dosed in units instead of mg?
Because the international unit is defined by biological activity, not mass. This keeps dosing consistent even though different insulins have slightly different molecular weights and potencies. Clinical insulin is always prescribed in units, never milligrams.
How do I convert insulin units to milligrams?
Multiply the number of units by the mg-per-unit factor for that insulin type. For human insulin: units × 0.0347 = mg, so 100 units ≈ 3.47 mg. This is for reference only — never dose insulin in mg.
How many units are in 1 mg of insulin?
About 28.8 units for human insulin (the inverse of 0.0347 mg per unit). Analog values vary slightly. This conversion is used in pharmacology and research, not clinical dosing.
Is insulin the same as Ozempic or semaglutide, which is dosed in mg?
No. Ozempic and Wegovy (semaglutide) and Mounjaro and Zepbound (tirzepatide) are GLP-1-based medicines, a different drug class from insulin, and they are dosed in milligrams. Insulin is always dosed in units. Don't apply an insulin units-to-mg conversion to those pens.
Does the mg per unit differ between insulin brands?
Slightly. Because each insulin has its own molecular weight, the mass per unit varies a little — human insulin and detemir are about 0.0347 mg/unit, while glargine is about 0.0364 mg/unit. The dose in units is what matters clinically, so these small mass differences don't change how you dose.
Sources
- WHO Expert Committee on Biological Standardization. 4th International Standard for Insulin (Human) — 1 mg ≈ 28.846 IU, i.e. 1 IU ≈ 0.0347 mg.
- Lantus (insulin glargine) U-100 Prescribing Information — each mL contains 100 units (3.6378 mg), i.e. 1 unit ≈ 0.0364 mg.
Last reviewed: June 2025