Mass Percent Calculator

Mass percent, also called percent by mass or weight percent, expresses how much of a mixture's total mass comes from a selected component. The formula is component mass divided by total mixture mass, multiplied by 100. Because the numerator and denominator are both masses, they must use the same unit, but that unit cancels in the ratio. Grams are shown in this calculator for convenience; kilograms, milligrams, or another consistent mass unit produce the same percentage. This calculator accepts several component masses as a comma-separated list. Each value is divided independently by the total mass, making it useful for a solution with one solute or a mixture containing several known substances. For a complete mixture, the component masses add to the total and their percentages add to 100 percent, apart from rounding. If only selected components are entered, the displayed percentages add to less than 100 percent and the unlisted remainder represents solvent or other material. Percent by mass is widely used because it does not change when temperature alters the volume of a liquid. Laboratory solution labels, alloy compositions, food formulations, environmental samples, and industrial blends often specify composition this way. For example, 5 g of sodium chloride in 100 g of final solution is 5 percent by mass. Notice that the denominator is the final solution mass, not merely the solvent mass. Adding 5 g of solute to 100 g of solvent creates 105 g of solution and therefore gives about 4.76 percent by mass. Measure every mass with suitable precision and account for the container by taring the balance. Use the actual final mass when evaporation, transfer loss, or reaction changes the amount present. The calculator rejects a listed component sum greater than the total because that combination cannot describe the same mixture. Report no more significant figures than the measurements support. This tool provides immediate composition checks, but analytical or regulated work should also document uncertainty, sample preparation, and the basis on which each component mass was determined.