At a glance
| Concentration | 2.5 mg is | Mark on U-100, 1 mL |
|---|---|---|
| 1 mg/mL | 2.5 mL | does not fit (over 1 mL) |
| 2.5 mg/mL | 1 mL | 100 |
| 5 mg/mL | 0.5 mL | 50 |
| 10 mg/mL | 0.25 mL | 25 |
| 20 mg/mL | 0.125 mL | 13 (exactly 12.5) |
Arithmetic at the concentrations shown. The concentration on your own label is the one that counts; enter it in the calculator.
Why the answer depends on the label
This question has no single answer; the concentration on your vial decides it. A milligram is an amount of medication. A syringe unit is a hundredth of a millilitre on a U-100 syringe. To go from one to the other you need the number that links amount to volume, which is the concentration in mg/mL printed on the vial or the pharmacy label. If your vial is a powder you reconstitute yourself, the concentration is the vial's mg divided by the millilitres of diluent you added. Once you know it, the arithmetic is two steps: millilitres equals milligrams divided by mg/mL, and units equals millilitres times 100. The examples in the table show how much the answer moves with concentration. A 2.5 mg dose spans from 12.5 units to the full 100-unit barrel across ordinary concentrations, so reading the label is not a formality. If the vial says micrograms rather than milligrams, remember that 2.5 mg is 2,500 mcg.
The mistake to watch for. If 2.5 mg at your concentration comes out above 100 units, it does not fit a 1 mL insulin syringe. Ask your pharmacist about a larger syringe or, for a powder vial, about a smaller diluent volume. Do not draw twice.