Protein Molecular Weight Calculator
Calculate protein molecular weight from amino acid composition or sequence
Calculate Protein Molecular Weight
Select amino acids and quantities manually
Amino Acid Composition
Protein Molecular Weight Results
Formula: Protein MW = Σ(Amino acid MW × count) - (18.0153 × (n-1))
Water molecules removed: 0 (for peptide bonds)
Conversion: 1 u = 1 Da = 0.001 kDa
Understanding Protein Molecular Weight
What is Protein Molecular Weight?
Protein molecular weight is the total mass of a protein molecule, calculated by summing the molecular weights of all amino acids and subtracting the mass of water molecules removed during peptide bond formation.
Why Calculate Protein MW?
- •Western Blot: Predict protein migration distance in gel electrophoresis
- •Protein Purification: Size-based separation techniques
- •Mass Spectrometry: Protein identification and verification
- •Drug Development: Understanding protein structure and function
Calculation Method
Protein MW = Σ(AA MW × count) - (18.0153 × (n-1))
- AA MW: Molecular weight of each amino acid
- count: Number of each amino acid
- 18.0153: Molecular weight of water (H₂O)
- n-1: Number of peptide bonds formed
Unit Conversions
Average Amino Acid Properties
Average MW
~110 Da per amino acid (including peptide bonds)
Range
Glycine (75 Da) to Tryptophan (204 Da)
Water Loss
18.0153 Da per peptide bond formed
Typical Protein Sizes
Note: This calculator provides theoretical molecular weight. Actual protein mass may vary due to post-translational modifications.