Peptide Molecular Weight Calculator

Mass = sum of residue masses + one water (H₂O). Average mass uses average atomic weights; monoisotopic mass uses the most abundant isotope of each element.

Assumptions: a linear peptide with a free N-terminus (H) and free C-terminus (OH). N-terminal acetylation adds C₂H₂O (+42.0106 Da monoisotopic). C-terminal amidation replaces OH with NH₂ (−0.9840 Da monoisotopic). Accepts one-letter codes (GHK) or three-letter codes separated by hyphens (Gly-His-Lys). Disulfide bonds, other modifications and non-standard residues are not included.

Worked example: Gly-Gly = 2 × 57.0519 + 18.0153 = 132.12 Da (average).