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Mass Percent Solution Calculator

Enter the solute and solvent masses to get the mass percent.

How it is calculated

Enter the mass of the dissolved substance (solute) and the mass of the liquid it is dissolved in (solvent), both in grams. The tool adds them to get the mass of the whole solution and divides: mass % = solute ÷ (solute + solvent) × 100. It reports the percentage with two decimals and the total solution mass in grams. The solvent mass is only the solvent, not the finished solution, so it must not already include the solute. A solvent mass of 0 is accepted and gives 100%. If the total mass is zero or negative, there is no result. Densities and volumes are not used, so the figure is weight per weight (w/w), not weight per volume.

Worked example

You dissolve 25 g of salt in 175 g of water. Total solution mass: 25 + 175 = 200 g. Fraction of solute: 25 ÷ 200 = 0.125. Multiply by 100: 12.50%. The tool also shows the total as 200.00 g. In other words, every 100 g of this brine contains 12.5 g of salt and 87.5 g of water.

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Common mistakes

  • Entering the total solution mass in the solvent field. If you weighed 200 g of finished solution containing 25 g of solute, the solvent is 175 g, not 200 g.
  • Mixing units, such as solute in milligrams and solvent in grams. The result assumes both fields are in the same unit, and the total is labelled grams.
  • Confusing w/w with w/v. A label such as 10 g per 100 mL is a mass-per-volume figure and cannot be typed in here as grams of solution.
  • Dividing the solute by the solvent only. That gives a ratio that is higher than the mass percent, because the solute is part of the denominator.

About this calculator

Mass percent (also written w/w%) expresses the concentration of a solution as the mass of solute divided by the total mass of the solution, multiplied by 100: mass % = [mass of solute ÷ (mass of solute + mass of solvent)] × 100. Unlike molarity, this measure doesn't depend on the solution's volume or temperature, since it's based purely on mass.

Chemistry students and lab technicians use mass percent to prepare solutions from a recipe — weighing out solute and solvent on a balance rather than measuring volume — and it's the standard concentration unit on commercial product labels: household bleach, hydrogen peroxide, and battery acid are all typically labeled by mass percent. It's especially convenient in industrial and food chemistry, where components are measured by weight throughout the process anyway.

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Comments (1)

  • Editorial team

    Recipes usually give the final batch weight, so work backwards before you weigh anything. For 500 g of a 5% solution you need 25 g of solute and 475 g of solvent; entering those two returns 5.00% and a total of 500.00 g. A common slip is adding 500 g of solvent to the 25 g, which gives 4.76% instead. What solution are you preparing?

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