Peptide calculator
Work out concentration, molarity and dilutions for peptide solutions at the bench. Pick a compound to fill in its molecular weight.
For laboratory solutions. Results assume 100% net peptide content; see below for how to correct for it.
How each calculation works
Concentration. Divide the mass of peptide by the volume of solvent. Molarity converts that mass concentration to a count of molecules, using the molecular weight.
c (mg/mL) = m (mg) ÷ V (mL) · c (mM) = c (mg/mL) ÷ MW (g/mol) × 1000
Dilution. The amount of peptide stays the same when you add diluent, so the product of concentration and volume is equal before and after.
C1 × V1 = C2 × V2 → V1 = C2 × V2 ÷ C1
Mass for a molarity. Multiply the target molarity by the volume to get the amount in micromoles, then by the molecular weight to get the mass.
n (µmol) = c (mM) × V (mL) · m (mg) = n (µmol) × MW (g/mol) ÷ 1000
Correcting for net peptide content
A vial labelled 10 mg holds 10 mg of powder, but not all of it is peptide. Salts left from synthesis, such as acetate or trifluoroacetate, and bound water make up part of the weight. Net peptide content is often 70–90%.
Where the lot certificate gives a net peptide content, multiply the label mass by it before calculating. At 80%, 10 mg of powder contains 8 mg of peptide.
Worked example
A 10 mg vial of BPC-157 (1419.5 g/mol) dissolved in 2 mL gives 5.00 mg/mL, or 3.52 mM. To make 10 mL at 1 mg/mL from that stock, take 2.00 mL of stock and add 8.00 mL of diluent.
Questions
How do you calculate peptide concentration?
Divide the mass of peptide by the volume of solvent. 10 mg in 2 mL gives 5 mg/mL, which is the same as 5,000 µg/mL.
How do you convert mg/mL to mM?
Divide the concentration in mg/mL by the molecular weight in g/mol, then multiply by 1,000. For BPC-157 at 5 mg/mL: 5 ÷ 1419.5 × 1000 = 3.52 mM.
What does C1V1 = C2V2 mean?
Stock concentration times stock volume equals final concentration times final volume. It lets you work out how much stock to take for any dilution.
Why does molecular weight matter?
Two peptides at the same mg/mL can hold very different numbers of molecules. Molarity lets you compare them on equal terms.
Where do the molecular weights come from?
Each one is the average mass of the free peptide from its library entry. Salt forms weigh more; check the lot certificate for the form supplied.