Reconstitution calculator
A reference tool for laboratory protocol preparation. Enter the vial contents and the volume you are adding.
Milligrams, from the vial label.
Millilitres.
Enter the amount, then pick the unit.
Result
| Concentration | - |
| Volume to draw | - |
| On a 100 unit insulin syringe | - |
Worked example
A 10 mg vial reconstituted with 2 mL of bacteriostatic water gives a concentration of 5 mg/mL. To draw 250 mcg (0.25 mg) from that solution you would draw 0.05 mL, which is 5 units on a 100 unit insulin syringe.
This calculator is arithmetic only. It is a preparation reference for laboratory work and it is not guidance for use in humans or animals.
How the arithmetic works
Two steps, and the second is where most errors happen.
Concentration. Divide the mass in the vial by the volume of diluent you add. A 10 mg vial plus 2 mL gives 5 mg/mL. Adding less diluent makes a stronger solution, not more material: the mass in the vial never changes, so the only thing you are choosing is how concentrated it is and therefore how small the volumes you will be drawing become.
Volume to draw. Divide the amount you want by the concentration. 0.25 mg from a 5 mg/mL solution is 0.05 mL. Keep the units consistent: mixing mcg and mg in the same calculation is the single most common way to end up an order of magnitude out.
Insulin syringe units are not millilitres
A U-100 insulin syringe is marked in units, where 100 units is 1 mL. So one unit is 0.01 mL, and the 0.05 mL above is 5 units. The markings say "units" because the syringe was designed for insulin, and that number has no relationship to the mass of anything else you put in it. Read it as hundredths of a millilitre and the confusion disappears.
Why it refuses some numbers
If the volume you would need to draw is larger than the volume in the vial, the calculator says so rather than returning a figure. That combination usually means the diluent volume or the units were entered wrong, and returning a plausible number for an impossible draw would hide the mistake instead of surfacing it.
Before you reconstitute
Work the numbers out before the vial is open, not after. Once diluent is in, the concentration is fixed for that vial. Let both vials reach room temperature, direct the stream against the glass rather than onto the solid, and do not shake it. The bacteriostatic water guide covers the diluent itself, including how long it lasts once the stopper is pierced.