How do I calculate peptide reconstitution?

Divide the peptide in the vial (mg) by the bacteriostatic water you added (mL) to get the concentration in mg/mL. Convert your target dose from micrograms to milligrams by dividing by 1000, then divide that by the concentration to get the volume in mL. Multiply by 100 to get units on a U-100 insulin syringe. Worked example: a 10 mg vial with 2 mL of water is 5 mg/mL; a 250 mcg dose is 0.25 mg; 0.25 ÷ 5 = 0.05 mL; ×100 = 5 units.

How much bacteriostatic water should I add to a vial?

There is no single correct amount — it is a trade-off. Less water makes a more concentrated solution, so each dose is a smaller number of units, which is harder to measure precisely. More water makes doses easier to read on the syringe but uses more volume per injection. A good target is a dose that lands somewhere between 10 and 50 units. The calculator flags a draw under 2 units as too small to measure reliably.

What does U-100 mean on an insulin syringe?

U-100 describes the graduation scale: 100 units equals 1 mL. So on any U-100 syringe, 1 unit is 0.01 mL regardless of whether the barrel holds 0.3 mL, 0.5 mL or 1 mL. This is why peptide doses are usually discussed in units — the conversion is constant.

Why does the calculator refuse to show a number sometimes?

Because a wrong dose figure is worse than no dose figure. If an input is zero, blank or not a number, there is no meaningful answer to give, so the calculator explains what to fix instead of rendering something that looks like a result. It also warns — while still showing the number — when a draw is under 2 units, when it will not fit the selected syringe, or when your dose is larger than the whole vial, which almost always means mg and mcg have been mixed up.

How long does reconstituted peptide last?

Once mixed, most peptides are kept refrigerated at 2–8°C and are commonly cited as usable for around 30 days, though this varies by compound and by the preservative in the water used. Bacteriostatic water contains benzyl alcohol, which inhibits bacterial growth; sterile water does not and gives a much shorter window. Each peptide page lists storage guidance for both the lyophilised powder and the reconstituted solution.

Free tool

Reconstitution calculator

Milligrams in the vial, millilitres of bacteriostatic water, micrograms per dose. Out comes the number of units to draw — plus the concentration and volume, so you can check it against your own arithmetic.

Your vial

Peptide in vial

As printed on the vial label

Bacteriostatic water added

How much you inject into the vial

Dose you want

mcg

1000 mcg = 1 mg

Syringe size

Start from a peptide

Fills in a common vial size and the low end of commonly cited protocols. Always check against your own vial.

Draw this much

5units

on a 1 mL U-100 insulin syringe

Concentration: 5 mg/mL
Volume: 0.05 mL
Doses in this vial: 40

Keep this vial. VialPal holds the concentration, counts down the doses left in it, and logs the ones you actually took.

VialPal does the arithmetic — it does not tell you what to take. Dose decisions belong between you and a qualified clinician.

The arithmetic

How it works, step by step.

01
Concentration
10 mg ÷ 2 mL = 5 mg/mL
Peptide in the vial divided by the water you added.
02
Dose in milligrams
250 mcg ÷ 1000 = 0.25 mg
Protocols are written in micrograms; concentration is in milligrams.
03
Volume to draw
0.25 mg ÷ 5 mg/mL = 0.05 mL
Dose divided by concentration.
04
Units on the syringe
0.05 mL × 100 = 5 units
A U-100 syringe has 100 units per millilitre.

Questions

Reconstitution calculator

How it works, step by step.

Concentration

Dose in milligrams

Volume to draw

Units on the syringe

Start from a specific peptide.

Reconstitution, explained.