🧬 Protein Molecular Weight Calculator
Estimate a protein’s molecular weight from its amino acid chain length using the average residue mass approximation.
How this estimate works
Every amino acid residue in a protein chain contributes, on average, about 110 daltons (Da) to the total molecular weight once peptide bonds have formed. Multiplying the number of residues by this average, and adding roughly 18 Da for the single water molecule associated with the chain’s two ends, gives a quick estimate of the whole protein’s molecular weight.
Why it’s an estimate
Real amino acids range from about 75 Da (glycine) to 204 Da (tryptophan), so the true molecular weight depends on the exact sequence composition. For an exact value, sum the residue masses of the specific sequence using a tool that reads the actual amino acid letters, or use mass spectrometry.
This calculator is intended for quick estimation and educational use, such as sanity-checking an expected band size on a gel.