Alloy Composition Calculator

Weight percent measures each element's share of the alloy's total mass, while atomic percent measures its share of the total number of atoms -- and those diverge whenever the elements have different atomic masses. A heavier element contributes more mass per individual atom, so it always registers a higher weight percent than atomic percent in the same alloy, while a lighter element shows the opposite pattern; only when all the elements happen to share identical atomic masses would the two percentages match.

Weight percent is calculated purely from the mass values you enter for each element, divided by their total mass -- atomic mass never enters that calculation at all. Atomic mass only comes into play when converting weight percent into mole counts for the atomic percent calculation, so adjusting an element's atomic mass (for example, to model a different isotope or to correct a data entry) changes its atomic percent without touching its weight percent.

Atomic percent is derived by converting each element's weight percent into a mole count -- dividing by atomic mass -- before re-normalizing across all elements. If an element's weight share stays the same but its atomic mass increases, that same mass now corresponds to fewer moles (fewer individual atoms), so its share of the total atom count, and therefore its atomic percent, goes down even though nothing about its weight contribution changed.

Set Element 3 Weight to 0 -- with zero mass contributed, it drops out of both the weight percent and atomic percent calculations entirely, leaving the results as a standard two-element conversion between Element 1 and Element 2. The Element 3 Atomic Mass field can be left at any value in that case, since a zero weight means it has no effect on the outcome either way.