Protein Molecular Weight

The 20 standard amino acids have wildly different residue masses, from glycine at 57 Da to tryptophan at 186 Da, so 110 Da is simply the rough population average used for a quick estimate without needing the actual sequence. This means the calculator will overestimate proteins rich in small residues like glycine and alanine, and underestimate proteins rich in large ones like tryptophan and arginine — it's meant for fast triage, not a substitute for a residue-by-residue sum or a mass spec measurement.

Like the residue mass, 100 Da is an average across modification types — phosphorylation adds about 80 Da while glycosylation can add anywhere from under 200 Da to well over 1,000 Da depending on the glycan structure. The calculator's Modification Mass output simply multiplies your modification count by this flat average, so it's a rough placeholder rather than a modification-specific calculation.

Not for real lab work. The extinction coefficient uses a fixed 120 per residue rather than being derived from your protein's actual tryptophan, tyrosine, and cystine content — the residues that actually govern 280 nm absorbance — and the isoelectric point is a hardcoded 6.5 that never changes regardless of your inputs. Both are included only as illustrative placeholders; use a sequence-based tool like ProtParam for values you'll rely on.

Those two outputs are exact, not estimates — one codon (three nucleotides) per amino acid residue you entered — but they intentionally represent only the coding sequence for the mature protein chain itself. Real mRNA also includes a start codon, a stop codon, and untranslated regions at both ends, none of which are counted here since the calculator only knows your amino acid count, not the full transcript structure.