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Mass Percent Calculator

Find a solution's mass percent concentration.

How it is calculated

The formula is mass percent = (msolute ÷ msolution) × 100. Both masses must be in the same unit (grams in the form), so the unit cancels and the result is a plain w/w percentage shown to two decimals. The mass of the solution is the solute plus the solvent, not the solvent alone. The solution mass must be above zero, the solute mass cannot be negative, and the solute cannot be larger than the solution: any of these gives no result, since a part cannot outweigh the whole. A solute equal to the solution gives 100.00%, and a solute of 0 gives 0.00%. Only mass is used, so density and volume play no part.

Worked example

You dissolve 15 g of salt in water and the finished solution weighs 250 g on the scale. Divide the solute by the solution: 15 ÷ 250 = 0.06. Multiply by 100 and the tool shows 6.00%. The water in the solution is 250 − 15 = 235 g. A 6.00% solution therefore holds 6 g of salt in every 100 g of solution.

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Common mistakes

  • Dividing by the solvent mass instead of the solution mass. With 15 g of salt in 235 g of water you would get 6.38% instead of 6.00%.
  • Mixing units, such as grams of solute and kilograms of solution. Both must be in the same unit.
  • Using volumes. Mass percent is w/w; 15 g in 250 mL is not the same as 15 g in 250 g, because a solution's density is rarely exactly 1.
  • Entering the solute mass larger than the solution mass. The tool shows no result, which usually means the two fields were swapped or the solvent mass was typed in the solution field.
  • Confusing mass percent with molarity or molality, which use moles and are not interchangeable with it.

About this calculator

This calculator finds a solution's mass percent concentration as (mass of solute ÷ mass of solution) × 100 — a concentration unit based purely on mass, distinct from molarity (moles per litre of solution) or molality (moles per kilogram of solvent), and often the easiest to measure directly on a lab or kitchen scale since it needs no molar mass or volume conversion. It's the same measurement behind everyday labels like “5% acetic acid” on vinegar or alcohol-by-weight figures on some beverages.

Chemistry students use it as an entry point into concentration units before moving to molarity and molality; pharmacists and lab technicians use it to prepare solutions and dilutions to an exact strength; and food scientists and manufacturers use it to calculate and label ingredient concentrations by weight.

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