Percentages are also commonly used to express the composition of mixtures, including solutions. The mass percentage of a solution component is defined as the ratio of the component’s mass to the solution’s mass, expressed as a percentage:

Mass percentage = (mass of component ÷ mass of solution) × 100%

The Mass percentage is also referred to by similar names such as percent mass, percent weight, weight/weight percent, and other variations on this theme. The most common symbol for mass percentage is simply the percent sign, %, although more detailed symbols are often used, including %mass, %weight, and (w/w) %.

Bleach has a concentration of 7.4% NaOCl by mass.