Estimate a protein’s molecular weight from its amino acid count.
The 110 Da average residue mass gives a quick estimate accurate to within a few per cent for most proteins. A 500-residue protein is therefore about 55 kDa, which matches typical gel behaviour. Molecular weight predicts migration on a denaturing gel, so a discrepancy is often the first sign of post-translational modification or proteolysis.
Protein Molecular Weight
MW ≈ 110 Da × residues + 18 Da for the terminal water
MW ≈ 110 Da × residues + 18 Da for the terminal water The 110 Da average residue mass gives a quick estimate accurate to within a few per cent for most proteins. A 500-residue protein is therefore about 55 kDa, which matches typical gel behaviour.
Molecular weight predicts migration on a denaturing gel, so a discrepancy is often the first sign of post-translational modification or proteolysis.
This calculator takes 3 inputs: Number of amino acids, Average residue mass, Quantity available. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.