This calculator answers the one question every reconstitution comes down to: how many units do I draw? Enter the milligrams of peptide in the vial, the volume of bacteriostatic water you added, and the dose you want in micrograms. It returns the mark to draw to on a standard insulin syringe, plus the resulting concentration.
The formula
Reconstitution is simple arithmetic once the units line up:
- Concentration (mcg/mL) = vial amount (mg) × 1000 ÷ water added (mL)
- Volume to inject (mL) = target dose (mcg) ÷ concentration (mcg/mL)
- Syringe units = volume (mL) × units-per-mL of your syringe (100 for U-100)
Example: 5 mg in 2 mL is 2500 mcg/mL. A 250 mcg dose is 0.1 mL — that is 10 units on a U-100 insulin syringe.
Why concentration matters more than the number
More water means a lower concentration and a larger, easier-to-measure volume — helpful for small doses. Less water means a higher concentration and less volume to inject. The peptide quantity is fixed; you are only choosing how to dilute it. This tool lets you try water volumes until the units land somewhere you can read precisely on your syringe.
Using this as a bacteriostatic water calculator
Because the amount of bacteriostatic water (BAC water) you add is what sets the concentration, this doubles as a bacteriostatic water calculator. Enter the peptide in the vial and your target dose, then adjust the BAC water figure: the tool shows how the concentration and the units-to-draw change with every millilitre of water. That lets you pick a water volume where the draw lands at a clean, readable mark on your insulin syringe.
For example, 5 mg of peptide reconstituted with 1 mL of BAC water gives 5000 mcg/mL, while the same 5 mg in 2 mL gives 2500 mcg/mL — the second draws twice the volume for the same dose, which is easier to measure. New to the diluent? See what is bacteriostatic water and choosing how much BAC water to use.