{
  "title": "PurePeptideHub Peptide Mass Calculator — method and reference examples",
  "url": "https://purepeptidehub.com/tools/peptide-mass-calculator",
  "methodId": "linear-free-termini-v1",
  "updatedAt": "2026-09-17",
  "convention": "Fixed University of Washington / Unimod CHNOS atomic masses",
  "scope": "Linear, unmodified sequences of the 20 standard amino acids, with free N- and C-termini and reduced cysteines. Neutral molecular mass only.",
  "formula": "Sum of amino-acid residue formulas + H2O; equivalently sum of free amino-acid formulas minus (length - 1) H2O.",
  "units": "Da",
  "precision": "Reference values are numerical calculations under the stated convention, not experimental measurement precision.",
  "limitations": [
    "No amidation, acetylation, cyclization, disulfide bonds, nonstandard residues or isotope labels.",
    "No charge-state, ion/adduct m/z, pI, hydrophobicity, digestion or molarity calculation.",
    "A matching theoretical mass does not establish identity, purity, amount, sterility or clinical suitability."
  ],
  "atomicMasses": [
    {
      "element": "C",
      "monoisotopic": 12,
      "average": 12.0107
    },
    {
      "element": "H",
      "monoisotopic": 1.007825035,
      "average": 1.00794
    },
    {
      "element": "N",
      "monoisotopic": 14.003074,
      "average": 14.0067
    },
    {
      "element": "O",
      "monoisotopic": 15.99491463,
      "average": 15.9994
    },
    {
      "element": "S",
      "monoisotopic": 31.9720707,
      "average": 32.065
    }
  ],
  "residueFormulas": {
    "A": [3, 5, 1, 1, 0],
    "R": [6, 12, 4, 1, 0],
    "N": [4, 6, 2, 2, 0],
    "D": [4, 5, 1, 3, 0],
    "C": [3, 5, 1, 1, 1],
    "E": [5, 7, 1, 3, 0],
    "Q": [5, 8, 2, 2, 0],
    "G": [2, 3, 1, 1, 0],
    "H": [6, 7, 3, 1, 0],
    "I": [6, 11, 1, 1, 0],
    "L": [6, 11, 1, 1, 0],
    "K": [6, 12, 2, 1, 0],
    "M": [5, 9, 1, 1, 1],
    "F": [9, 9, 1, 1, 0],
    "P": [5, 7, 1, 1, 0],
    "S": [3, 5, 1, 2, 0],
    "T": [4, 7, 1, 2, 0],
    "W": [11, 10, 2, 1, 0],
    "Y": [9, 9, 1, 2, 0],
    "V": [5, 9, 1, 1, 0]
  },
  "residueFormulaElementOrder": ["C", "H", "N", "O", "S"],
  "examples": [
    {
      "sequence": "G",
      "label": "One glycine: free termini",
      "formula": "C2H5NO2",
      "monoisotopic": 75.032028435,
      "average": 75.0666
    },
    {
      "sequence": "AG",
      "label": "One peptide bond",
      "formula": "C5H10N2O3",
      "monoisotopic": 146.06914224,
      "average": 146.1445
    },
    {
      "sequence": "CC",
      "label": "Two reduced cysteines",
      "formula": "C6H12N2O3S2",
      "monoisotopic": 224.02893371,
      "average": 224.30108
    },
    {
      "sequence": "M",
      "label": "Sulfur-containing methionine",
      "formula": "C5H11NO2S",
      "monoisotopic": 149.051049345,
      "average": 149.21134
    },
    {
      "sequence": "IL",
      "label": "Isoleucine and leucine",
      "formula": "C12H24N2O3",
      "monoisotopic": 244.17869273,
      "average": 244.33056
    },
    {
      "sequence": "PEPTIDE",
      "label": "A seven-residue example",
      "formula": "C34H53N7O15",
      "monoisotopic": 799.359964305,
      "average": 799.82252
    },
    {
      "sequence": "ACDEFGHIKLMNPQRSTVWY",
      "label": "All 20 standard residues",
      "formula": "C107H159N29O30S2",
      "monoisotopic": 2394.124906865,
      "average": 2395.71366
    }
  ],
  "sources": [
    {
      "title": "University of Washington Proteomics Resource: formulas and masses",
      "url": "https://proteomicsresource.washington.edu/resources/data-analysis/masses/"
    },
    {
      "title": "Unimod: atomic mass conventions",
      "url": "https://www.unimod.org/masses.html"
    }
  ]
}