Units to mL Calculator
Volume to give
– mL
Enter a dose in units and the strength on the vial.
- Strength
- –
- Dose
- –
The working
This works out the arithmetic. The order, the product in your hand and local policy still govern what is given.
Units are not milligrams
An international unit measures how much biological effect a substance produces, not how much it weighs. It was defined this way because insulin, heparin and several vitamins were in clinical use before anyone could purify or weigh them reliably, and the definition stuck.
The practical consequence is that there is no conversion factor between units and milligrams. A search for how many mg are in a unit has no answer, in the same way that a search for how manymg are in a mL has no answer without a strength. A dose in units can only meet a strength written in units per mL.
How to convert units to mL
volume in mL = dose in units ÷ units per mL
With standard U-100 insulin, 100 units in every millilitre:
| Dose | Volume of U-100 |
|---|---|
| 100 units | 1 mL |
| 50 units | 0.5 mL |
| 30 units | 0.3 mL |
| 20 units | 0.2 mL |
| 10 units | 0.1 mL |
| 5 units | 0.05 mL |
| 2 units | 0.02 mL |
U-100, U-200 and U-500 insulin
Concentrated insulins exist so that large doses fit in a manageable volume. The same 50-unit dose:
| Insulin | Strength | Volume for 50 units |
|---|---|---|
| U-100 | 100 units/mL | 0.5 mL |
| U-200 | 200 units/mL | 0.25 mL |
| U-500 | 500 units/mL | 0.1 mL |
U-500 is fivefold concentrated, and drawing it up as though it were U-100 delivers five times the intended dose. It is one of the products most often named in medication safety alerts for exactly this reason.
Why insulin syringes are graduated in units
An insulin syringe is marked in units for one specific concentration, so the dose on the chart is the number on the barrel and no conversion happens at all. That removes the arithmetic step this page exists to perform, which is why an insulin syringe is what should be used whenever one is available.
The volume shown above is for checking and for the situations where a unit-graduated syringe is not to hand. It is not an argument for drawing insulin up in a millilitre syringe by choice.
Questions about units and millilitres
- How many units are in 1 mL of insulin?
- In standard U-100 insulin, 100 units. Concentrated insulins exist at U-200 and U-500, holding two and five times as much in the same millilitre, so the strength has to be read off the pen or vial rather than assumed.
- How do I convert units to mL?
- Divide the dose in units by the units per mL on the vial. 30 units of U-100 insulin is 30 ÷ 100, or 0.3 mL.
- How many mg is a unit of insulin?
- There is no conversion. A unit measures biological activity, not weight. Milligrams and units are different kinds of quantity, so a dose in units can only be worked out against a strength given in units per mL.
- Why should insulin be drawn up in an insulin syringe?
- An insulin syringe is graduated in units for a specific concentration, so the dose is read directly and no conversion happens. Drawing insulin into a millilitre syringe introduces an arithmetic step that is a well-documented source of large overdoses.