Percent Composition Calculator

Percent composition expresses how much of a compound, mixture, or sample is contributed by one component. Mass percent is calculated by dividing the component mass by the total sample mass and multiplying by one hundred. The result answers a straightforward question: out of every one hundred units of sample mass, how many units belong to the selected component? It is widely used for chemical formulas, alloy specifications, nutrition, mineral analysis, solution preparation, and manufacturing quality control. For a pure compound, elemental percent composition can be calculated from its chemical formula. Multiply each element's atomic mass by the number of its atoms in one formula unit, then divide that contribution by the compound's molar mass. In water, oxygen contributes approximately 16.00 grams to a molar mass of about 18.015 grams, producing roughly 88.8 percent oxygen by mass. The hydrogen contribution makes up the remainder. Minor differences in atomic-weight tables and rounding can slightly change the final digits. For a physical mixture or solution, use measured masses instead. If five grams of salt are present in a solution whose total mass is 125 grams, the salt concentration is four percent by mass. The total must include the component and every other material. Adding five grams of solute to 120 grams of solvent creates 125 grams of solution, not 120 grams. Confusing solvent mass with solution mass is a common source of error. Component and total masses may use grams, kilograms, milligrams, or another mass unit, but both values must use the same unit because they form a ratio. The component cannot exceed the total when both describe the same sample. Individual component percentages should sum to approximately one hundred percent for a complete composition, though rounding and unmeasured trace material can create a small difference. A single component may legitimately be zero percent but total mass must be greater than zero. Mass percent differs from volume percent, mass-to-volume percent, mole percent, and parts per million. These concentration measures use different denominators and should not be substituted without density or molecular information. Always report the basis along with the numerical percentage. This calculator specifically evaluates mass divided by mass. It provides a fast, transparent ratio for coursework and routine analysis, while the accuracy of the result remains limited by sample purity, representative sampling, instrument precision, and the reliability of the entered masses.