Protein Molecular Weight Calculator
Estimate a protein’s molecular weight from its amino acid count.
About Protein Molecular Weight Calculator
The 110 Da average residue mass gives a quick estimate accurate to within a few per cent for most proteins. A 500-residue protein is therefore about 55 kDa, which matches typical gel behaviour. Molecular weight predicts migration on a denaturing gel, so a discrepancy is often the first sign of post-translational modification or proteolysis.
Formula
Protein Molecular Weight
MW ≈ 110 Da × residues + 18 Da for the terminal water
- 110 Da
- Average amino acid residue mass across typical proteins
- kDa
- Kilodaltons, the conventional unit for protein size
Worked example
With the default values below, Protein Molecular Weight Calculator returns Molecular Weight of 55.0180. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Number of amino acidsminimum 0
- 500
- Average residue massminimum 1 Da
- 110 Da
- Quantity availableminimum 0 ug
- 50 ug
Results
- Molecular Weight
- 55.0180 kDa
- Molecular Weight
- 55,018.0 Da
- Amount
- 0.90879 nmol
- Number of Molecules
- 547,288,229,306,772
- Conversion Factor
- 55.01800 ug/nmol
Step by step
- 1Values used
- 2Protein Molecular Weight
- 3Molecular Weight= 55.0180 kDa
- 4Molecular Weight= 55,018.0 Da
- 5Amount= 0.90879 nmol
- 6Number of Molecules= 547,288,229,306,772
- 7Conversion Factor= 55.01800 ug/nmol
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Protein Molecular Weight calculated?
MW ≈ 110 Da × residues + 18 Da for the terminal water The 110 Da average residue mass gives a quick estimate accurate to within a few per cent for most proteins. A 500-residue protein is therefore about 55 kDa, which matches typical gel behaviour.
Why does Protein Molecular Weight matter?
Molecular weight predicts migration on a denaturing gel, so a discrepancy is often the first sign of post-translational modification or proteolysis.
What values do I need to enter?
This calculator takes 3 inputs: Number of amino acids, Average residue mass, Quantity available. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.