At a glance
| Volume | U-100, 1 mL mark | U-40, 1 mL mark |
|---|---|---|
| 0.05 mL | 5 | 2 |
| 0.1 mL | 10 | 4 |
| 0.2 mL | 20 | 8 |
| 0.25 mL | 25 | 10 |
| 0.3 mL | 30 | 12 |
| 0.5 mL | 50 | 20 |
| 0.75 mL | 75 | 30 |
| 1 mL | 100 | 40 |
Arithmetic at the concentrations shown. The concentration on your own label is the one that counts; enter it in the calculator.
Why the marks mean volume
The word "units" on an insulin syringe is a volume scale, designed so that one unit of U-100 insulin is one mark. Because U-100 insulin is 100 units per mL, the scale runs 100 marks per mL. That is why a 1 mL syringe reads 0 to 100, a 0.5 mL syringe reads 0 to 50, and a 0.3 mL syringe reads 0 to 30. All three use the same scale; only the length of the barrel changes, which is why the smaller syringes are easier to read for small draws. A U-40 syringe is a different scale: 40 marks per mL, made for veterinary insulins that are 40 units per mL. The two syringes look alike, so the U-rating printed on the box and barrel is the thing to check. When a medication other than insulin is drawn with an insulin syringe, the marks still measure volume in hundredths of a millilitre, and they say nothing about the medication's own units, milligrams or IU. Converting a dose to a mark always goes through the concentration on the vial label.
The mistake to watch for. The 100 mark on a U-100 syringe is 1 mL of anything. It is 100 units of U-100 insulin only because that insulin is 100 units per mL. For any other medication, the mark you draw to depends on the concentration printed on your vial.