Energy & Environment

Protein Molecular Weight (from Sequence)

Compute a protein's molecular weight in daltons and kilodaltons from its amino acid sequence, or estimate quickly from residue count. It also reports tryptophan and tyrosine counts for absorbance work.

How to use
  1. Paste the amino acid sequence, or enter a residue count.
  2. The calculator sums standard average residue masses.
  3. Check the Trp and Tyr counts for the 280 nm coefficient.
Estimates based on typical values; your real usage and rates will vary.
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How it's calculated

MW = Σ (residue masses) + 18.015

Sum of average amino-acid residue masses (e.g. Gly 57.05, Ala 71.08 Da) across the sequence plus one water molecule (18.015 Da) for the free termini. Extinction coefficient ε₂₈₀ ≈ 5500·(Trp) + 1490·(Tyr); 1 kDa = 1000 Da.

Common questions

How is protein molecular weight calculated?

It sums the average mass of each amino acid residue in the sequence, plus one water molecule for the free ends.

Why do Trp and Tyr counts matter?

Tryptophan and tyrosine drive a protein's absorbance at 280 nm, so their counts set the extinction coefficient used to measure concentration.

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