Amino Acid Molecular Weight Calculator

Type a sequence to calculate molecular weight and composition instantly online. Switch between monoisotopic and average modes with precise hydration handling and capping. Add common modifications like phosphorylation, acetylation, amidation, or labels for flexible workflows. Export results as CSV or PDF for documentation purposes.

Input

Supported: A,R,N,D,C,E,Q,G,H,I,L,K,M,F,P,S,T,W,Y,V and B,Z,J,X approximations.
Positive or negative; added to total mass.

Formula Used

Total mass = Σ(residue masses) + mass(H2O) + terminal caps + Σ(modification deltas).

  • Residue masses are peptide-form values (free amino acid minus H2O).
  • Mass(H2O) = 18.01056 Da (monoisotopic) or 18.01528 Da (average).
  • N-acetylation adds +42.010565 Da; C-amidation adds −0.984016 Da (monoisotopic).
  • Common deltas: phosphorylation +79.966331 Da; oxidation +15.994915 Da; carbamidomethyl +57.021464 Da (monoisotopic).

How to Use

  1. Paste or type a sequence using one-letter amino acid codes.
  2. Select the desired mass type: monoisotopic or average.
  3. Toggle terminal capping and specify modification counts if applicable.
  4. Click Calculate to view results; export using CSV or PDF.

Residue Mass Reference

ResidueMonoisotopic (Da)Average (Da)
A71.0371171.0788
R156.10111156.1875
N114.04293114.1038
D115.02694115.0886
C103.00919103.1388
E129.04259129.1155
Q128.05858128.1307
G57.0214657.0519
H137.05891137.1411
I113.08406113.1594
L113.08406113.1594
K128.09496128.1741
M131.04049131.1926
F147.06841147.1766
P97.0527697.1167
S87.0320387.0782
T101.04768101.1051
W186.07931186.2132
Y163.06333163.1760
V99.0684199.1326

Modification Mass Deltas

Modification / TerminiMonoisotopic Δ (Da)Average Δ (Da)
Phosphorylation79.96633179.9799
Oxidation15.99491515.9994
Carbamidomethyl57.02146457.0513
N-terminus Acetylation42.01056542.0367
C-terminus Amidation-0.984016-0.9840
Water (peptide termini)18.01056468418.01528

Ambiguous Codes and Approximations

  • B is averaged between D and N residue masses.
  • Z is averaged between E and Q residue masses.
  • J equals I or L; both have identical masses here.
  • X uses a placeholder of 110.0000 Da; verify experimentally.

Results

Enter a sequence and click Calculate to see results.

Example Data

SequenceLengthModeMass (Da)
ACDEFGHIK9MONO1018.454195
PEPTIDE7MONO799.359945
MKWVTFISLL10AVG1237.565880

Notes

  • Ambiguous codes B, Z, J are averaged between possibilities.
  • X is treated as 110.0000 Da; review before final reporting.
  • Carbamidomethyl typically targets cysteines; counts are user-specified here.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.