For lab and research use
Peptide Molarity Calculator
Convert between mass and molar concentration for a peptide solution. Enter the molecular weight from your certificate of analysis.
Peptide molarity calculator
Example values are loaded. Replace them with the numbers on your own vial.
Use the exact value on your certificate of analysis, including any salt form.
The formulas
Concentration (mM) = amount (µmol) ÷ volume (mL)
Mass to weigh (mg) = target (mM) × volume (mL) × MW (g/mol) ÷ 1,000
Example: 5 mg of a peptide with a molecular weight of 1,419.5 g/mol is 3.522 µmol. Dissolved in 1 mL, that is 3.522 mM (3,522 µM).
Use the molecular weight on your certificate
The same peptide can have different molecular weights depending on its salt form (acetate, trifluoroacetate, hydrochloride) and any modifications. Peptide content is also rarely 100%: net peptide content on a certificate of analysis is often 70–90% of the powder weight. For precise work, multiply the weighed mass by the net peptide content before calculating.
Frequently asked questions
What is the difference between mM and µM?
1 mM (millimolar) equals 1,000 µM (micromolar). Both are moles of substance per litre of solution.
Why does my certificate of analysis list a different molecular weight?
Salt forms and modifications change the molecular weight. Always use the value for the exact material you have.