Protein Molecular Weight, pI & Properties Calculator
Compute molecular weight, isoelectric point, extinction coefficient and composition.
🔒 Runs entirely in your browser — nothing is uploaded
Paste a protein sequence to compute its molecular weight, theoretical isoelectric point (pI), net charge at pH 7, molar extinction coefficient at 280 nm, GRAVY hydropathy and full amino-acid composition. It is a quick ProtParam-style readout for designing expression constructs, planning purification, or estimating protein concentration from absorbance — calculated entirely in your browser.
0 residues · non amino-acid characters are ignored
Values use average residue masses, the EMBOSS pKa set for pI and net charge, and Edelhoch extinction coefficients. Treat them as close estimates — exact figures depend on modifications, buffer and method.
How to use the Protein Properties tool
- 1Paste a protein sequence using one-letter amino-acid codes (FASTA accepted).
- 2Read the molecular weight, theoretical pI, charge and extinction coefficient.
- 3Use ε₂₈₀ and A(0.1%) to convert A280 absorbance into protein concentration.
Frequently asked questions
- How is the isoelectric point (pI) calculated?
- The pI is the pH at which the protein's net charge is zero. It is found by solving the charge equation with standard side-chain pKa values (the EMBOSS set) plus the N- and C-termini.
- How do I use the extinction coefficient?
- Divide your measured A280 by the A(0.1%) value to get concentration in mg/mL, or divide by the molar ε₂₈₀ (after accounting for path length) to get molar concentration. We report values for reduced cysteines and for cysteines forming cystines.
- Which amino acids are recognised?
- The 20 standard amino acids in one-letter code. Other characters (spaces, numbers, ambiguity codes) are ignored so pasted sequences work without cleanup.