Free tool

Peptide calculator

Three quick calculators: work out the concentration after reconstituting a vial, the exact syringe volume for a target dose, and the molecular weight of a peptide from its sequence. Everything runs in your browser — nothing is sent anywhere.

Read this first

This is a math aid for educational use, not medical or dosing advice, and Chemdu does not sell or recommend injectable peptides. Only use a medicine as directed by a licensed clinician, and always follow the dosing on your prescription. Double-check every number before it matters.

1 · Reconstitution calculator

You have a vial of peptide powder and some bacteriostatic water. This tells you the concentration once mixed.

2 · Dose → syringe volume

Given the same mix, this tells you how much to draw for a target dose — in mL and in insulin-syringe units (U-100).

3 · Molecular weight from sequence

Enter a peptide’s one-letter amino-acid sequence (e.g. YGGFM) to get its average molecular weight, length and composition.

How the reconstitution math works

Reconstitution just means dissolving a freeze-dried (lyophilised) peptide powder in liquid — usually bacteriostatic water. The concentration is simply the amount of peptide divided by the volume of water:

  • Concentration (mg/mL) = peptide (mg) ÷ water (mL)
  • Concentration (mcg/mL) = that number × 1000
  • Volume for a dose = dose (mcg) ÷ concentration (mcg/mL)
  • Insulin units (U-100) = volume (mL) × 100 — because a U-100 syringe reads 100 units per mL

Adding more water makes the solution more dilute, so you draw a larger, easier-to-measure volume for the same dose — a common reason people reconstitute with 2–3 mL rather than 1 mL.

Frequently asked questions

Sterile water containing a small amount of benzyl alcohol that inhibits bacterial growth, letting a reconstituted vial be used over multiple days. It’s used for many injectable medicines under a clinician’s direction.
A standard U-100 insulin syringe is marked so that 100 units = 1 mL. So 0.25 mL is 25 units, 0.5 mL is 50 units, and so on. This calculator shows both.
No — the total peptide in the vial is fixed. More water only changes the concentration, and therefore the volume you draw for a given dose. It doesn’t create more or less peptide.
It uses average residue masses summed with one water molecule, giving the average molecular weight of the free (unmodified) peptide — the number you’ll usually see quoted for a sequence.

Related reading

How to reconstitute peptides → Peptides, explained → Therapeutic peptides →

Not medical advice. Chemdu is an educational resource and does not sell, prescribe or supply any peptide. These calculators are provided as-is for general education. Always follow a licensed clinician’s instructions for any medication.