Molecular Weight Calculator
Calculate the neutral molecular weight of a peptide or protein from its amino acid sequence. Select average mass for an isotope-weighted estimate or monoisotopic mass for a calculation using the principal isotope of each element. Both results are reported in daltons.
Results
Calculate a valid sequence to see its theoretical mass.
How molecular weight is calculated
Add the residue masses from the ExPASy FindMod reference table and one water molecule for the two free termini. The selected mass mode determines both the residue masses and the mass of water. Results display four decimal places.
Read the calculation method →Worked example
ACD
Average mass 307.3214 Da. Monoisotopic mass 307.0838 Da.
Limitations
- One neutral, linear, unmodified chain with free N- and C-termini. Cysteines are modeled without disulfide bonds.
- Use the result as a neutral theoretical mass. Comparing it with an observed mass-to-charge peak requires accounting for the ion charge and any adducts.