Average vs. Monoisotopic Mass
Compare isotope-weighted and monoisotopic peptide masses and see how the two calculations differ for the same sequence.
What the two values represent
Average mass weights the isotopes of each element by their abundance in the reference composition. Monoisotopic mass uses the most abundant isotope of each element. Both calculator values describe a neutral molecule and are reported in daltons.
Compare the same sequence in both modes
The peptide ACD gives 307.3214 Da in average mode and 307.0838 Da in monoisotopic mode. The calculator uses the residue masses and terminal water correction from the same mode throughout.
Compare like quantities
Match the mass convention used by the reference you are comparing against. If the reference is a peak on a mass spectrum, first account for charge state and any adducts to compare it with a neutral mass.