Protein MW, pI & extinction

Paste a protein sequence or FASTA to compute average molecular weight, isoelectric point (pI), GRAVY hydropathy, net charge at pH 7, amino-acid composition, and A₂₈₀ extinction coefficients (Pace et al.). Useful before western blots, molarity calculations, and recombinant protein work.

All calculations run in your browser. Pair the molecular weight with the molarity calculator when preparing stocks, or inspect structure in the PDB 3D viewer.

Protein sequence or FASTA

Run the calculator to see MW, pI, extinction, GRAVY, and composition.

How this tool works

This is a browser implementation of classic ProtParam-style protein parameters used when you need molecular weight for gels and stocks, pI for buffer choice, or A₂₈₀ for concentration without uploading sequences to a remote server.

Molecular weight

Average residue masses are summed and one water molecule is added for the terminal groups (same convention as ExPASy ProtParam). Results are in daltons (g/mol for the intact polypeptide).

Isoelectric point and charge

pI is the pH where net charge is zero, found by binary search using Bjellqvist side-chain and terminus pKa values. Charge at pH 7 uses the same model — helpful for estimating migration and solubility trends, not a substitute for measured zeta potential.

Extinction coefficient

ε₂₈₀ follows Pace et al. (1995): Trp 5500, Tyr 1490, and cystine 125 M⁻¹ cm⁻¹. Reduced ignores Cys; oxidized counts floor(Cys/2) cystines. Abs 0.1% (= 1 g/L) is ε / MW. Proteins without Trp or Tyr need another assay (Bradford, BCA, etc.).

Limitations and privacy

Average isotopic masses; not monoisotopic MS exact masses.
No PTMs, disulfide topology beyond the cystine count heuristic, or prosthetic groups.
Sequences stay in your browser; nothing is sent to The Bond Lab servers.