Percentage by mass, also known as mass percent or percent by mass, is a way of expressing the concentration or composition of a substance by comparing the mass of a specific component to the total mass of the compound or mixture, then multiplying by 100 to get a percentage. The formula for percentage by mass is:
% by mass=(mass of componenttotal mass of compound or mixture)×100%%\text{ by mass}=\left(\frac{\text{mass of component}}{\text{total mass of compound or mixture}}\right)\times 100%% by mass=(total mass of compound or mixturemass of component)×100%
This measure is commonly used in chemistry to express the amount of an element in a compound or the amount of a solute in a solution by mass. For example, to find the percent by mass of zinc in a compound, you would divide the mass of zinc by the total mass of the compound and multiply by 100%. The percentages of all components typically add up to 100%. This concept is important for understanding the composition of materials, for nutritional information on food labels, and for calculating empirical formulas in chemistry.