This Peptide Chemical Calculator application is a tool to calculate the molecular formulae, accurate mono isotopic and average masses of your peptide.
You can work with a sequence in one- or three-letter amino acid code, choose few popular modifications on N- and C-terminals or add disulfide bridges.

The masses are calculated using the following atomic weights:

H Element Monoisotopic mass - 1.0078250
Average mass - 1.0079400
C Element Monoisotopic mass - 12.0000000
Average mass - 12.0110000
N Element Monoisotopic mass - 14.0030740
Average mass - 14.0067400
O Element Monoisotopic mass - 15.9949146
Average mass - 15.9994000
F Element Monoisotopic mass - 18.9984033
Average mass - 18.9984000
P Element Monoisotopic mass - 30.9737634
Average mass - 30.9737600
S Element Monoisotopic mass - 31.9720718
Average mass - 32.0660000
Cl Element Monoisotopic mass - 34.9688527
Average mass - 35.4527000
Br Element Monoisotopic mass - 78.9183361
Average mass - 79.9040000