Want the numbers without the maths? Use the free peptide molarity and dilution calculator — enter mass, molecular weight and volume to get concentration and molarity instantly. This guide explains the calculations behind it.
A peptide calculator does three jobs at the bench: it tells you the concentration of a solution you have made, converts mass into molarity, and works out how to dilute a stock to working strength. All three are below, with the formulas behind them, worked examples and a reference table of molecular weights.
These tools are for in-vitro laboratory solutions. They are not dosing calculators, and nothing here is guidance for preparing anything for human or animal use.
The short answer
- Concentration (mg/mL) = peptide mass (mg) ÷ solvent volume (mL).
- Molarity (mM) = 1,000 × mass (mg) ÷ [molecular weight (g/mol) × volume (mL)].
- Dilution: C₁ × V₁ = C₂ × V₂, so the stock volume you need is V₁ = C₂ × V₂ ÷ C₁.
- For true peptide concentration, multiply the powder mass by its net peptide content first, because a vial labelled 10 mg is rarely 10 mg of peptide.
Concentration calculator
Peptide concentration
Mass of lyophilized powder dissolved in a known volume of solvent. Leave net peptide content at 100 if you don’t know it.
Molarity calculator
Molar concentration
Use the molecular weight from your certificate of analysis where possible, or the reference table below.
Dilution calculator
Stock to working solution (C₁V₁ = C₂V₂)
Use the same concentration unit for stock and target, for example mg/mL for both.
Worked examples
1. Concentration
You dissolve 10 mg of lyophilized peptide in 2 mL of solvent. The concentration is 10 ÷ 2 = 5 mg/mL, or 5,000 µg/mL. If the certificate shows a net peptide content of 80%, only 8 mg of the powder is peptide, so the true peptide concentration is 8 ÷ 2 = 4 mg/mL.
2. Molarity
You dissolve 5 mg of Epitalon, molecular weight about 390.3 g/mol, in 1 mL. Molarity = 1,000 × 5 ÷ (390.3 × 1) = 12.8 mM. The same 5 mg of a peptide ten times heavier would give roughly a tenth of that molarity, which is why molar comparisons between peptides need the molecular weight.
3. Dilution
You need 10 mL of a 0.1 mg/mL working solution from a 5 mg/mL stock. V₁ = 0.1 × 10 ÷ 5 = 0.2 mL of stock, topped up with 9.8 mL of diluent. For very large dilution factors, a two-step serial dilution is usually more accurate than one large step.
Every compound below ships with a batch-matched COA showing its tested mass and purity.
Browse the catalogueMolecular weight reference table
Approximate molecular weights for common research peptides, as free peptides. Salt forms and chemical modifications such as N-acetylation change the value, so use the figure on your certificate of analysis when it is available.
| Peptide | Length | Molecular weight (g/mol) |
|---|---|---|
| KPV | 3 residues | 342.4 |
| Epitalon | 4 residues | 390.3 |
| Pinealon | 3 residues | 418.4 |
| Selank | 7 residues | 751.9 |
| Semax | 7 residues | 813.9 |
| GHRP-2 | 6 residues | 818.0 |
| DSIP | 9 residues | 848.8 |
| GHRP-6 | 6 residues | 873.0 |
| Hexarelin | 6 residues | 887.0 |
| Kisspeptin-10 | 10 residues | 1,302.4 |
| Sermorelin | 29 residues | 3,357.9 |
| CJC-1295 (no DAC) | 29 residues | 3,367.9 |
| LL-37 | 37 residues | 4,493.3 |
Five common calculation mistakes
- Mixing units. Milligrams and micrograms differ by a factor of 1,000, and so do millilitres and microlitres. Convert everything before you calculate.
- Treating label mass as peptide mass. Lyophilized powder contains counter-ions and water as well as peptide. Our guide to net peptide content and salt forms explains why.
- Using the wrong molecular weight. An acetylated or amidated peptide, or a salt form, has a different mass from the free peptide.
- Diluting in the wrong direction. In C₁V₁ = C₂V₂, the stock is always the more concentrated solution.
- Rounding early in serial dilutions. Small rounding errors compound at every step. Keep full precision until the final value.
Accurate maths starts with accurate inputs, which is why a certificate of analysis that reports measured mass and purity matters. For the handling side of solution work, see our lab tools page and peptide storage guide.
Lab-tested research peptides to work with
The calculator works for any lyophilized peptide in our catalogue. Janoshik test reports for each product below are listed on our Lab Testing page, so you can check purity and identity before you weigh anything out.
BPC-15715-amino-acid research peptideView product
TB-500Thymosin beta-4 research peptideView product
GHK-CuCopper tripeptideView product
EpithalonLyophilized tetrapeptideView product
Research use only. These calculators are for preparing in-vitro laboratory solutions. Pure Peptides Canada products are not for human or veterinary use, and nothing on this page is dosing, administration or medical guidance.
Frequently asked questions
What is a peptide calculator?
A peptide calculator is a tool for the arithmetic of laboratory solutions: the concentration of a dissolved peptide, its molarity from mass and molecular weight, and the volumes needed to dilute a stock to a working concentration.
How do I calculate peptide concentration?
Divide the mass of peptide in milligrams by the volume of solvent in millilitres to get mg/mL. For true peptide concentration, first multiply the powder mass by its net peptide content.
How do I convert mg/mL to molarity?
Molarity in mM equals 1,000 × mass in mg ÷ (molecular weight in g/mol × volume in mL). Equivalently, divide the mg/mL concentration by the molecular weight and multiply by 1,000.
What does C1V1 = C2V2 mean?
It is the dilution equation: stock concentration times stock volume equals final concentration times final volume. Rearranged, the stock volume needed is V1 = C2 × V2 ÷ C1, and the rest of the final volume is diluent.
Why does net peptide content matter?
Lyophilized peptides contain counter-ions and water as well as peptide, so the powder mass overstates the peptide mass. Ignoring that makes every concentration you calculate too high.
Is this a dosing calculator?
No. These calculators are for in-vitro laboratory solutions only. Pure Peptides Canada products are research reagents that are not for human or veterinary use, and we do not provide dosing guidance.
Lab-tested research peptides, documented batch by batch
Every batch is tested by Janoshik Analytical and ships with a batch-matched COA, tracked across Canada with pricing in Canadian dollars.
For laboratory research use only. Not for human or veterinary use. Calculations are provided for in-vitro solution preparation and are not medical, dosing or administration advice.