At a glance
| Volume | U-100, 1 mL mark | U-100, 0.3 mL mark | U-40, 1 mL mark |
|---|---|---|---|
| 0.05 mL | 5 | 5 | 2 |
| 0.1 mL | 10 | 10 | 4 |
| 0.15 mL | 15 | 15 | 6 |
| 0.2 mL | 20 | 20 | 8 |
| 0.25 mL | 25 | 25 | 10 |
| 0.3 mL | 30 | 30 | 12 |
| 0.5 mL | 50 | does not fit | 20 |
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
Ten units is where the two meanings of "unit" are easiest to confuse, because for insulin they agree. Ten units of U-100 insulin is the 10 mark, 0.1 mL, and nobody needs to think about it. The moment the vial holds something else, the mark still means 0.1 mL but the dose is 0.1 mL times the concentration: 0.5 mg at 5 mg/mL, 100 units of HCG at 1,000 units per mL, 1 mg at 10 mg/mL. The U-40 syringe is the other trap. Its 10 mark is 0.25 mL, two and a half times the volume, because the scale has 40 marks to the millilitre. U-40 insulin drawn to 10 on a U-40 syringe is 10 units; U-100 insulin drawn to the same mark on that syringe is 25 units.
The mistake to watch for. On a 1 mL syringe the 10 mark is close to the needle and the lines are two units apart, so 10 is a numbered line but 9 and 11 are not. If your dose is an odd number of units, the 0.5 mL or 0.3 mL syringe shows every unit.