Protein Length From Gene Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Protein Length From Gene Calculator
Every three bases of a coding sequence (a codon) specifies one amino acid - this calculator converts coding sequence length directly into expected protein length.
Total Codons = Coding Sequence Length / 3
Amino Acids = Total Codons - 1 (excluding the stop codon)
Example
A 300 bp coding sequence (including start and stop codons):
Total Codons = 300 / 3 = 100 → 99 amino acids in the resulting protein
Why Subtract One?
Every protein-coding gene ends with a stop codon (UAA, UAG, or UGA in mRNA) that signals the ribosome to terminate translation - the stop codon doesn't code for an amino acid, which is exactly why the final protein always has one fewer amino acid than the total codon count in the coding sequence.
What About the Start Codon?
The start codon (AUG) does encode an amino acid - methionine - which becomes the first amino acid of the initial polypeptide chain. In many mature proteins this initial methionine is later cleaved off by cellular processing enzymes, but it's still counted as part of the originally translated protein in this calculation.