Calculate
Enter values and run the tool.
Result
Formula and method
Average molecular mass = the sum of documented average amino-acid residue masses plus one terminal water molecule (18.01524 Da). The calculation uses one consistent average-mass system.
Worked example
A single alanine residue is 71.0788 + 18.01524 = 89.09404 Da under this convention.
Limits and assumptions
Supports the 20 standard amino acids. It excludes post-translational modifications, disulfide changes, glycosylation, phosphorylation, isotope labels, nonstandard residues, multimers, and terminal modifications.
Method sources
SIB ExPASy mass values supplies the average residue masses and water mass. ExPASy Compute pI/Mw documentation describes summing average amino-acid masses and one water molecule.