Peptide molecular weight calculator
Enter a sequence in one-letter amino-acid codes to get its molecular formula, average mass and monoisotopic mass. Load any of our sequences, or add terminal modifications and disulfide bonds.
How it works
Each amino acid in a chain contributes a residue: the amino acid minus the water lost when the peptide bond forms. The calculator adds the residue formulas for your sequence, adds one water for the free ends, then applies any modifications. Acetylating the N-terminus adds C₂H₂O; amidating the C-terminus swaps OH for NH₂ (+H +N −O); each disulfide bond removes two hydrogens.
Average mass uses standard atomic weights. It matches what you weigh, and it is the figure to use for concentration. Monoisotopic mass uses the most abundant isotope of each element. It matches the main peak in a mass spectrum.
Worked example: BPC-157
The sequence GEPPPGKPADDAGLV has 15 residues. Summing them and adding water gives C62H98N16O22, an average mass of 1419.54 g/mol and a monoisotopic mass of 1418.7042 Da. These match PubChem and the 1419.53 g/mol on our BPC-157 certificate.
Next, use the average mass in the solution concentration calculatorto convert between mg/mL and molarity. Each figure is checked against PubChem for the preset sequences. Non-standard residues, such as the Dmt in SS-31, aren't supported.
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