Percentage Composition
The proportion by mass of each element in a compound, expressed as a percentage of the total mass.
Formula / equation
% element = (n × A_r / M_r) × 100
Unit
Dimensionless
In depth
Percentage composition follows directly from the formula and molar masses, and running the calculation in reverse converts elemental analysis data into an empirical formula. It is also used commercially to specify fertiliser grades and ore assays.
Examples in the real world
In water, hydrogen is (2 × 1.008 / 18.02) × 100 = 11.19% and oxygen is 88.81% by mass.