Using the reconstitution calculator.

Reconstitution math is simple arithmetic that is easy to get wrong under pressure, usually because three different units are in play at once. The calculator removes the arithmetic. It does not decide any of the numbers, all three of which come from you.

The three inputs.

• •Vial strength: how much compound is in the vial, from the label, usually in milligrams
• •Diluent volume: how much bacteriostatic water you are adding, in millilitres
• •Target amount: the amount per dose you and your provider have settled on, usually in micrograms or milligrams

Strength divided by volume gives concentration. Your target amount divided by that concentration gives a volume to draw, which the calculator then expresses in U-100 syringe units, because that is the scale printed on the syringe you are holding. It also draws the result on a syringe illustration so you can check the mark against the number.

Changing the water changes everything.

The volume of diluent is a choice, and it is the lever most people underuse. More water gives a more dilute solution and a larger, easier-to-measure draw; less water gives a small draw where a fraction of a unit matters. The compound quantity does not change either way. If your target keeps landing between marks, recomputing with a different diluent volume usually fixes it.

The four mistakes that produce wrong answers.

1. 01Mixing micrograms and milligrams. One milligram is one thousand micrograms, and this is the error behind most tenfold mistakes.
2. 02Treating syringe units as millilitres. On a U-100 syringe, 100 units is 1 mL, so 10 units is 0.1 mL.
3. 03Using the syringe's nominal size instead of its scale. A 0.5 mL insulin syringe is still marked in U-100 units, up to 50 of them.
4. 04Reusing a saved result after changing how much water you added. Redo the calculation whenever the diluent volume changes.

What the calculator will not do.

It will not suggest a target amount, will not fill one in, and has no default. It converts numbers you enter and nothing else. Storage, sterility, handling, and whether a given preparation is appropriate at all are outside what arithmetic can answer.