Mass Percent Calculator
The mass percent concentration: mass of solute ÷ mass of solution × 100.
Result
Mass percent (%)
25.00
How it works
Mass percent expresses how much of a solution's weight is the dissolved substance: solute mass ÷ total solution mass × 100. Dissolve 5 g of salt in 95 g of water and the solution weighs 100 g, so it is 5% salt by mass. The denominator is the trap. It is the mass of the whole solution — solute plus solvent — not the solvent alone. Using 5 ÷ 95 gives 5.26%, which is wrong; the solute is part of what you are dividing by. Mass percent is the concentration of choice when temperature must not matter: unlike volume-based measures, masses do not expand or contract when a solution warms up. That is why it dominates food labels, pharmaceutical formulations and industrial recipes, where a batch must be reproducible whatever the weather.
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Frequently asked questions
Is it the same as w/w?
Yes — mass percent is often written % w/w (weight for weight).
What is the solution mass?
The solute plus the solvent together — the whole mixture.
What is the difference from molarity?
Mass percent is a mass-to-mass ratio and ignores what the molecules are. Molarity counts moles of solute per litre of solution, so it depends on molar mass and on volume — and therefore on temperature.
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