Protein Molecular Weight Calculator
Compute molecular weight, isoelectric point, extinction coefficient and composition.
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 provides a ProtParam-style readout for designing expression constructs, planning purification, or estimating protein concentration from absorbance.
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.
Design, edit, and verify complete constructsSeqStudio combines sequence editing and annotation, plasmid maps, primer/cloning/CRISPR design, Sanger verification, and GenBank/SnapGene files in one workspace.
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.
- 3Enter a measured A280 to read the protein concentration in mg/mL and µM.
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?
Type the A280 you measured under the results, with its path length and any dilution, and the page converts it to mg/mL and µM by Beer–Lambert (c = A / ε·l), once for reduced cysteines and once for cysteines forming cystines. By hand: A280 ÷ A(0.1%) gives mg/mL, and A280 ÷ ε₂₈₀ gives the molar concentration.
Which amino acids are recognized?
The 20 standard amino acids in one-letter code. Other characters (spaces, numbers, ambiguity codes) are ignored so pasted sequences work without cleanup.
More
Guides
References
One-letter and three-letter amino acid codes with key properties.
Side-chain and terminal pKa values and how they set the isoelectric point.
Kyte-Doolittle, Hopp-Woods and Eisenberg values for all 20 amino acids, with the window sizes and transmembrane threshold each scale is read with.