Protein Molecular Weight Calculator

This tool takes a protein sequence in one-letter code and adds up the residue masses, plus the single water the chain keeps at its ends. It returns the average and monoisotopic molecular weight, the molecular formula, the amino acid composition, the extinction coefficient at 280 nm and the theoretical pI, and a second action turns an A280 reading into mg/mL. Everything comes from the sequence alone, checked on every run against ubiquitin and lysozyme. A signal peptide, a His tag, glycosylation or any other modification will move the real mass away from this figure.