Insulin syringe sizes: 0.3 mL, 0.5 mL and 1 mL
Updated 24 October 2026
U-100 insulin syringes come in three sizes. All three use the same scale, 100 units per mL, so 10 units is 0.1 mL on each of them. What changes is how much they hold and how finely they are marked.
| Syringe | Holds | Usual marks | Suits doses of |
|---|---|---|---|
| 0.3 mL | 30 units | every 1 unit; some every half unit | up to 30 units |
| 0.5 mL | 50 units | every 1 unit | 31–50 units |
| 1 mL | 100 units | every 2 units | 51–100 units |
Markings vary by brand. Read the scale on your own syringe before you draw a dose.
Pick the smallest syringe that holds the whole dose
A 5-unit dose is one small line on a 1 mL syringe marked every 2 units, but five clear lines on a 0.3 mL syringe. The FDA asks prescribers and pharmacies to give patients the syringe size that fits the intended dose and to show them how to measure it (FDA). In the reports behind that alert, patients drew 50 units when their dose was 5.
U-40 syringes: same look, different scale
U-40 syringes are made for pet insulin and hold 40 units in 1 mL, so each unit is 0.025 mL instead of 0.01 mL. Following U-100 instructions with a U-40 syringe gives two and a half times the dose: 10 units becomes 0.25 mL instead of 0.1 mL. Check for "U-100" on the syringe and the box.
Syringes marked in mL
Some instructions use a regular syringe marked in mL instead of units. Lilly's instructions for Zepbound vials, for example, show a 1 mL syringe filled to the 0.5 mL line. 0.5 mL is the same volume as 50 units on a U-100 syringe, but follow the syringe and the instructions your prescriber gave you. To convert between the two, see units to mL.