What peptide sequences are supported?

Enter 1 to 200 standard amino acid residues using single-letter codes. Ambiguous codes such as B, J, O, U, X, and Z are rejected.

What is the difference between monoisotopic and average mass?

Monoisotopic mass uses specific isotope masses and is commonly used for short peptides in high-resolution MS. Average mass reflects natural isotope abundance and is useful for longer chains.

Which peptide ions does the calculator report?

It reports the neutral mass M and the m/z values for [M+H]+, [M+Na]+, and [M+2H]2+.

Are spaces or separators allowed in a sequence?

Yes. Sequence input is case-insensitive, and spaces or separators are ignored.

Can this calculator replace experimental measurements?

No. It provides theoretical mass estimates for education and experimental planning, not measured instrument results.

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Peptide Mass Calculator (Monoisotopic/Average)

Sums ProtParam residue masses for a peptide sequence (mono or average) and reports M, [M+H]⁺, [M+Na]⁺, [M+2H]²⁺. Educational use only.

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2 examples

Angiotensin II (DRVYIHPF) — monoisotopic 1045.5345 Da

Angiotensin II has the sequence DRVYIHPF. Summing the eight monoisotopic residue masses and adding H₂O gives M = 1045.5345 Da, so the commonly observed ESI ion is [M+H]⁺ = 1046.5418 — matching the textbook value quoted in peptide MS tutorials.

{"result":"DRVYIHPF (8 residues) monoisotopic: M = 1045.5345 Da, [M+H]+ = 1046.5418, [M+Na]+ = 1068.5237","metadata":{"result":{"neutralMass":1045.5345,"protonatedMh":1046.5418,"length":8}}}

GGFL — average mass 392.4550 Da

The tetrapeptide Gly-Gly-Phe-Leu is a classic synthesis standard. With average natural-abundance masses the neutral mass is 392.4550 Da and the sodium adduct [M+Na]⁺ sits at 415.4443 — often the dominant species in MALDI spot checks.

{"result":"GGFL (4 residues) average: M = 392.455 Da, [M+H]+ = 393.4623, [M+Na]+ = 415.4443","metadata":{"result":{"neutralMass":392.455,"sodiatedMNa":415.4443,"length":4}}}

Inputs

Set the required fields, then run the tool.

3 options

ContentPaste or type the main input values.1

Peptide SequencetextRequiredSingle-letter amino acid codes; 1–200 residues.

SettingsAdjust formats, ranges, numbers, and modes.2

Mass TypeselectRequiredMonoisotopic for short peptides in HRMS; average for longer chains.Decimal PlacesnumberOptional

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Peptide Mass Calculator (Monoisotopic/Average)

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Key facts

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Use cases

Examples

1. Angiotensin II monoisotopic mass check

2. GGFL average mass estimate

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