Peptide reconstitution calculator: vial mg + BAC water → U-100 units.

How it works

The math, in one line.

dose volume (mL) = target dose (mg) ÷ (vial mg ÷ BAC water mL)

On a U-100 insulin syringe, 1 unit equals 0.01 mL. So a 0.05 mL dose is 5 units. A 0.10 mL dose is 10 units. The most common error is treating “units” as “milligrams”. They measure different things, and only line up coincidentally at one specific concentration.

For a longer walkthrough with worked examples, read semaglutide & tirzepatide reconstitution calculator.

Common questions

Peptide reconstitution, answered.

What's the peptide reconstitution formula?

Dose volume (mL) = target dose (mg) ÷ (vial mg ÷ BAC water mL). Multiply mL × 100 to get U-100 syringe units. The formula works for any peptide with a known vial mass.

What is BAC water?

Bacteriostatic water is sterile water with 0.9% benzyl alcohol added as a preservative. The benzyl alcohol prevents bacterial growth in the vial after the rubber stopper has been punctured. Use only BAC water for peptide reconstitution; sterile water without preservative spoils faster.

What is a U-100 insulin syringe?

A syringe graduated in units where 1 unit = 0.01 mL. Designed for U-100 insulin (1 unit = 0.01 mL = 1 unit of insulin activity). For peptides, the units are just a volume marking — treating units as milligrams is the most common dosing error in compounded GLP-1.

Why does my dose volume change after a refill?

Your prescriber writes a dose in milligrams; the pharmacy chooses the BAC water volume. A 5 mg vial reconstituted in 1 mL gives 5 mg/mL; the same 5 mg vial in 2 mL gives 2.5 mg/mL. Your prescribed dose in mg is the same. Your dose volume — and the units you draw — are not.

Does this calculator work for BPC-157?

Yes. The formula is the same regardless of compound. A 5 mg BPC-157 vial in 2 mL BAC water gives 2.5 mg/mL; a 250 mcg dose is 0.1 mL = 10 units. BPC-157 has no FDA approval — confirm dosing with your provider.

Does this calculator work for tirzepatide?

Yes, and there is a dedicated tirzepatide page with worked examples for 30 mg, 60 mg, and 120 mg vials at /tools/tirzepatide-reconstitution-calculator.

Does this calculator work for semaglutide?

Yes, and there is a dedicated semaglutide page with worked examples for 5 mg and 10 mg vials at /tools/semaglutide-reconstitution-calculator.

Is this calculator free?

Yes. No account, no email, runs in your browser. The iOS app extends the calculator with dose logging, plasma-decay charts, side-effect anchoring, and multi-compound stacks — also free to start with optional Pro at $9.99/mo or $49.99/yr.