How do you calculate peptide reconstitution?

Divide the peptide mass in the vial by the volume of solvent added to get the stock concentration. For example, 10 mg of peptide in 2 mL of bacteriostatic water gives 5 mg/mL (5,000 mcg/mL). To find the volume to withdraw for a target amount, divide the target amount by that concentration: a 250 mcg target from a 5,000 mcg/mL stock needs 0.05 mL, which is 5 units on a U-100 insulin syringe.

How much bacteriostatic water should I use to reconstitute a peptide?

The solvent volume is a choice, not a fixed rule — more water gives a more dilute stock and a larger, easier-to-measure draw volume; less water gives a concentrated stock and a smaller draw. Common laboratory practice is 1–3 mL per vial. Enter your chosen volume in the calculator to see the resulting concentration and draw size, then adjust until the draw lands on a convenient syringe graduation.

How many units on an insulin syringe is my target amount?

A U-100 insulin syringe is graduated so that 100 units equals 1 mL. Multiply the volume to withdraw (in mL) by 100 to get units. The calculator does this automatically and shows both the volume in mL and the equivalent U-100 units for the amount you enter.

What is the difference between mg and mcg here?

1 milligram (mg) equals 1,000 micrograms (mcg). Peptide vials are usually labelled in mg (e.g. 5 mg, 10 mg), while target amounts are often expressed in mcg. The calculator accepts either unit for the target amount and converts internally.

Is this calculator for human dosing?

No. This tool performs laboratory reconstitution math for research reference materials intended for in-vitro use only. It is not medical guidance and does not describe or authorize any human or animal use.

Peptide Reconstitution Calculator

Enter the peptide mass in the vial, the volume of bacteriostatic water you're adding, and the amount you want to withdraw. The calculator returns the stock concentration, the exact volume to draw, and the equivalent graduation on a U-100 insulin syringe — the standard math for reconstituting a lyophilized research reference material.

How the calculation works

Reconstitution math is two divisions. First, the stock concentrationis the peptide mass in the vial divided by the volume of solvent added — 10 mg of peptide in 2 mL of solvent is a 5 mg/mL (5,000 mcg/mL) stock. Second, the volume to withdrawfor a target amount is that amount divided by the concentration: a 250 mcg target from a 5,000 mcg/mL stock is 0.05 mL.

Because a U-100 insulin syringe is graduated at 100 units per millilitre, multiplying the withdrawal volume by 100 converts it to units — 0.05 mL is 5 units. The calculation assumes the lyophilized powder contributes negligible volume, so the final solution volume equals the solvent volume you add.

Concentration (mg/mL) = peptide mass (mg) ÷ solvent volume (mL)
Draw volume (mL) = target amount ÷ concentration
U-100 units = draw volume (mL) × 100

Choosing your reconstitution volume

The volume of solvent is a deliberate choice. A larger volume produces a more dilute stock and a larger, easier-to-measure withdrawal; a smaller volume produces a concentrated stock and a smaller draw. Neither is inherently correct — the goal is a draw volume that lands on a clean syringe graduation and a total that a vial can supply across the number of withdrawals you plan. Adjust the solvent volume in the calculator and watch the draw size and draws-per-vial update.

The choice of solvent matters as much as the volume. Bacteriostatic water — sterile water with 0.9% benzyl alcohol — is the usual choice when one vial will be sampled repeatedly, because the preservative suppresses microbial growth across multiple withdrawals. See the companion guides on bacteriostatic water and peptide reconstitution for the full method.