Protein Molecular Weight Calculator
Calculate the molecular weight of a protein or peptide from its one-letter amino acid sequence.
Enter a sequence above and click Calculate.
Formula
Average Molecular Weight:
MW = Σ(residue average masses) + H₂O − (2 × nSS × MH)
where H₂O = 18.01524 Da accounts for the free N- and C-termini, and each disulfide bond removes 2 hydrogen atoms (2 × 1.00794 Da).
Monoisotopic Molecular Weight:
MWmono = Σ(residue monoisotopic masses) + 18.01056 − (2 × nSS × 1.007825)
Molar Extinction Coefficient at 280 nm (Pace et al.):
ε₂₈₀ = (nTrp × 5500) + (nTyr × 1490) + (nSS × 125) [M⁻¹cm⁻¹]
Absorbance at 280 nm (1 mg/mL):
A₂₈₀ = ε₂₈₀ / MWavg
Assumptions & References
- Pace, C.N. et al. (1995) Protein Science 4:2411–2423. doi:10.1002/pro.5560041120