Peptide Calculator – Reconstitution & U-100 Units

Work out how many units to draw on a U-100 syringe after reconstituting a lyophilised peptide with bacteriostatic water. Enter the peptide in the vial, the water you added and the amount you want per draw; the calculator shows the syringe reading, the concentration and how many draws the vial holds. Switch tabs to work backwards and find how much water to add.

Peptide in vial Amount printed on the vial label

Bacteriostatic water added Total volume you inject into the vial

Amount per draw Peptide you want in each withdrawal

Syringe size U-100: 100 units = 1 mL

Draw to

—

Enter an amount per draw to see the syringe reading.

—Concentration

—Per 1 unit

—Draws per vial

Need bacteriostatic water? Sterile, 0.9% benzyl alcohol, in 3, 10, 20 and 30 mL multi-dose vials.

Shop bac water

For research and laboratory calculations only (RUO). Double-check every figure against your vial label and protocol. This tool does not recommend amounts and is not medical advice; Herbilabs products are not for human or veterinary use.

How the peptide calculator works

Three steps turn a vial label into a syringe reading:

Concentration = peptide in vial ÷ water added (5,000 mcg ÷ 2 mL = 2,500 mcg/mL).
Volume per draw = amount per draw ÷ concentration (250 mcg ÷ 2,500 mcg/mL = 0.1 mL).
U-100 units = volume × 100 (0.1 mL = 10 units).

Remember: 1 mg = 1,000 mcg. Most errors come from mixing the two, so check the unit selector next to each field.

Reconstitution tips for the lab

Let the vial reach room temperature, wipe both stoppers with an alcohol swab and add the water slowly down the side of the glass.
Swirl gently until clear; do not shake.
Label the vial with the date and concentration and store it refrigerated. See how long bac water lasts after opening.

Frequently asked questions

How many units is 1 mL on a U-100 syringe?

On a U-100 syringe, 100 units equals 1 mL, so 10 units is 0.1 mL and 1 unit is 0.01 mL. The calculator converts every result to U-100 units.

How do I calculate how many units to draw?

Divide the peptide in the vial by the water added to get the concentration. Then divide the amount you want per draw by that concentration to get millilitres, and multiply by 100 for U-100 units. Example: 5 mg in 2 mL is 2,500 mcg per mL, so 250 mcg is 0.1 mL, or 10 units.

How much bacteriostatic water should I add to a peptide vial?

There is no single right amount; it depends on how large you want each draw to be. More water makes each draw larger and easier to measure. Use the “How much water to add” tab: enter the peptide amount, the amount per draw and the units you want per draw.

Does adding more water change the amount of peptide?

No. The total peptide in the vial stays the same. More water only lowers the concentration, so you draw more units to get the same amount.

Why use bacteriostatic water instead of sterile water?

Bacteriostatic water contains 0.9% benzyl alcohol, which inhibits bacterial growth, so a multi-dose vial can be re-entered for up to 28 days with aseptic handling. Sterile water has no preservative and is meant for single use.