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 the dose from your instructions 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. Arithmetic example with arbitrary numbers: a 6 mg vial with 3 mL of water is 2 mg/mL; 500 mcg is 0.5 mg; 0.5 ÷ 2 = 0.25 mL; ×100 = 25 units.

How much bacteriostatic water should I add to a vial?

Use the reconstitution volume in your instructions or the product labelling. The arithmetic behind the choice: less water makes a more concentrated solution, so the same amount is a smaller number of units, which is harder to measure precisely; more water makes the units easier to read but means more volume. 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

Enter the milligrams in your vial, the millilitres of bacteriostatic water you added and the dose from your instructions. Out comes the number of units — 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 water you add to the vial

Dose from your instructions

mcg

From your clinician, pharmacy, product instructions, or research protocol. 1000 mcg = 1 mg

Syringe size

Fill in a vial size

Fills in a vial size this compound is commonly sold in. It does not fill in a dose — check the size against your own vial label.

Draw this much

Enter your numbers

Still needed: vial strength, bacteriostatic water, dose. Use the figures on your vial label and the dose from your clinician, pharmacy, product instructions, or research protocol — VialPal handles the math.

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

Get VialPal

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
6 mg ÷ 3 mL = 2 mg/mL
Peptide in the vial divided by the water you added.
02
Dose in milligrams
500 mcg ÷ 1000 = 0.5 mg
Doses are usually written in micrograms; concentration is in milligrams.
03
Volume to draw
0.5 mg ÷ 2 mg/mL = 0.25 mL
Dose divided by concentration.
04
Units on the syringe
0.25 mL × 100 = 25 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

Peptide reference pages.

Reconstitution, explained.