Peptide Reconstitution Math, Explained

The three formulas

Steps 2 and 3 combine into one line: units = dose × water × 100 ÷ vial, with the dose and vial in the same unit (both mg or both mcg).

Worked example 1: mg dose

15 mg vial, 3 mL of water, 2.5 mg dose. Concentration: 15 ÷ 3 = 5 mg/mL. Volume: 2.5 ÷ 5 = 0.5 mL. Units: 0.5 × 100 = 50 units.

Worked example 2: mcg dose

5 mg vial, 2 mL of water, 250 mcg dose. First convert: 250 mcg = 0.25 mg. Concentration: 5 ÷ 2 = 2.5 mg/mL. Volume: 0.25 ÷ 2.5 = 0.1 mL. Units: 10 units.

Worked example 3: choosing the water

10 mg vial, 0.5 mg dose, and you want each dose to be 10 units. Rearranging: water = units × vial ÷ (dose × 100) = 10 × 10 ÷ (0.5 × 100) = 2 mL. The BAC water calculator does this for you.

A mental shortcut

On a U-100 syringe, mcg per unit = concentration in mg/mL × 10. At 2.5 mg/mL each unit holds 25 mcg; at 5 mg/mL, 50 mcg; at 10 mg/mL, 100 mcg. Divide your dose in mcg by that number and you have the units.

Five mistakes worth checking for

1. mg and mcg mixed up. A thousandfold error. The dose must always be smaller than the whole vial.
2. Using the vial's total mg as the concentration. "10 mg vial" is the total, not mg per mL, unless the label says "mg/mL".
3. A U-40 syringe with U-100 math. Each unit holds 2.5 times more. Use mL instead.
4. Rounding too early. Round only the final units, and round to a mark your syringe actually has.
5. Forgetting the water already in a pre-mixed vial. For a solution labelled "2.5 mg/mL", enter 2.5 mg with 1 mL of water.

Every calculator on this site shows these steps under "Show the math", so you can check the working line by line.