Mass Percent Calculator

What is Mass Percent?

Mass percent (also called percent by weight, % w/w, or mass fraction expressed as a percentage) is a way of expressing the concentration of a solution. It tells you how many grams of solute are present in every 100 grams of solution. Because it is a ratio of masses, it is independent of temperature.

Mass Percent vs Other Concentration Units

Mass percent is one of several ways to describe how concentrated a solution is. Unlike molarity, it does not require knowing the molar mass of the solute or the volume of the solution.

• Mass percent (% w/w): grams of solute per 100 g of solution. Temperature-independent.
• Volume percent (% v/v): volume of solute per 100 mL of solution, common for liquid-liquid mixtures.
• Molarity (mol/L): moles of solute per liter of solution. Depends on volume and therefore temperature.
• Molality (mol/kg): moles of solute per kilogram of solvent. Like mass percent, it is temperature-independent.
• Parts per million (ppm): milligrams of solute per kilogram of solution; effectively mass percent × 10,000.

Worked Example

Note: This calculator assumes the masses entered are in the same physical units and that the solution mass equals the sum of solute and solvent. It does not account for any mass lost during preparation. Always weigh solute and solvent with an appropriately precise balance.

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