Protein Molecular Weight Calculator
Calculate protein molecular weight with our free science calculator. Uses standard scientific formulas with unit conversions and explanations.
Formula
MW = Sum of all residue weights + 18.015 Da (water)
Each amino acid residue contributes its specific molecular weight (ranging from 57 Da for glycine to 186 Da for tryptophan). One water molecule (18.015 Da) is added to account for the free N-terminal amino group and C-terminal carboxyl group. For estimates, use 110 Da per residue average. The extinction coefficient uses the Pace method: E280 = nTrp x 5500 + nTyr x 1490 + nCys x 125.
Frequently Asked Questions
How is protein molecular weight calculated from an amino acid sequence?
Protein molecular weight is calculated by summing the molecular weights of all individual amino acid residues in the sequence, then adding the molecular weight of one water molecule (18.015 Da). During peptide bond formation, one water molecule is lost per bond, but the N-terminus retains an extra hydrogen and the C-terminus retains an extra hydroxyl group, which together equal one water molecule. The average molecular weight of an amino acid residue is approximately 110 Da (after water loss), so a rough estimate is: MW = number of residues x 110. For precise calculations, each residue type has a specific weight ranging from 57 Da (Glycine) to 186 Da (Tryptophan).
What is the average molecular weight of an amino acid?
The average molecular weight of a free amino acid is about 128 Da, but in a protein (after peptide bond formation and water loss), the average residue weight is approximately 110-111 Da. This average varies slightly depending on the amino acid composition. Glycine-rich proteins (e.g., collagen) have lower average residue weights (~85 Da for Gly residue), while tryptophan-rich proteins are heavier. The 110 Da average is commonly used for quick estimates: a 300-residue protein is approximately 33 kDa. For precision, always use the exact sequence-based calculation rather than the estimate.
Can I use Protein Molecular Weight Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.
Is Protein Molecular Weight Calculator free to use?
Yes, completely free with no sign-up required. All calculators on NovaCalculator are free to use without registration, subscription, or payment.
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You can bookmark the calculator page in your browser. Many calculators also display a shareable result summary you can copy. The page URL stays the same so returning to it will bring you back to the same tool.
Does Protein Molecular Weight Calculator work offline?
Once the page is loaded, the calculation logic runs entirely in your browser. If you have already opened the page, most calculators will continue to work even if your internet connection is lost, since no server requests are needed for computation.