Protein Molecular Weight Calculator
Calculate protein molecular weight from amino acid composition. Converts between daltons (Da), kilodaltons (kDa), and megadaltons (MDa). Used in biochemistry, protein analysis, and molecular biology.
Formula
MW = (AA Count × Avg Weight) - (AA Count - 1) × 18.01528 (water loss)
- MW = (Amino Acid Count × Average Weight) - (AA Count - 1) × 18.01528
- Water (18.01528 Da) is removed during peptide bond formation
- Average amino acid weight: ~110 Da (varies by amino acid composition)
- 1 kDa = 1,000 Da
- Used to identify proteins via mass spectrometry
Example
Inputs
- Number of Amino Acids: 100
- Average Weight per AA (Da): 110
Protein with 100 amino acids at 110 Da average: MW = (100 × 110) - 99 × 18.01528 ≈ 10,218 Da ≈ 10.2 kDa.
Frequently asked questions
Why subtract water mass?
Peptide bonds form by removing water (H2O). Each bond removes 18.01528 Da from the theoretical sum.
What's an average amino acid weight?
~110 Da for typical proteins. Varies based on composition (glycine ~75 Da, tryptophan ~204 Da).