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Reconstitution calculator.

Vial strength and bacteriostatic water in, units-per-click out. No account, nothing to download.

Syringe

How the math works

Reconstitution is two divisions and a multiplication, which is exactly why it's easy to get quietly wrong at 6am.

Adding bacteriostatic water to a lyophilised vial gives you a concentration: the vial's strength divided by the volume of water. A 10 mg vial with 2 mL of water is 5 mg/mL. The water volume does not change how much peptide you have, only how concentrated it is.

To get a dose, divide it by that concentration. A 250 mcg dose (0.25 mg) at 5 mg/mL is 0.05 mL of liquid.

Insulin syringes aren't marked in millilitres, they're marked in units: 100 graduations per mL on a U-100. So 0.05 mL is 5 units. That last step is the one people skip, and it's a factor-of-100 error when they do.

"Units" here means syringe graduations, not international units. They are unrelated measures that share a name, and conflating them is its own category of mistake.

Getting it wrong in the safe direction

More water is not more drug, it just spreads the same peptide across a bigger volume, which means more units drawn for the same dose. That's usually the safer way to be imprecise, because small errors on a longer draw matter proportionally less.

If the calculator says your draw is more than the barrel holds, it will tell you. That's the failure worth catching: it means the numbers don't fit the syringe you picked, not that you should draw twice.

The water itself

Bacteriostatic water is sterile water with 0.9% benzyl alcohol added, which is what lets one vial be drawn from for 28 days rather than once. What it is, how it differs from the preservative-free sterile water sold beside it, how long it lasts after the first puncture, and how the label says to store it are covered on the bacteriostatic water page.

Calculators by compound

Each of these opens pre-filled with the vial size, water volume, and reported dose the REGEN catalog carries for that compound. Compounds taken orally or topically, and the ones dosed in international units rather than by mass, are not listed: there is no vial to reconstitute, or the arithmetic here cannot express their dose.

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