Mass Percent Calculator

Mass percent is the mass of a solute divided by the total mass of the solution, multiplied by 100. It answers what fraction of the whole mixture, by weight, is the dissolved substance. It is also called percent by mass or weight percent.

Mass percent equals mass of solute divided by mass of solution, times 100. The tool prints this as mass % = solute mass / solution mass x 100. When you give a solvent mass instead, the solution mass is solute plus solvent.

Use whichever you measured. In Solvent mass mode the tool adds solute and solvent to form the solution. In Solution mass mode you enter the total directly, which is handy when you weighed the finished mixture rather than the pure solvent.

The labels say grams, but the ratio is unitless, so any consistent unit gives the same percentage. If you enter both masses in kilograms or ounces the answer is identical, though the Solution mass tile will then be in that same unit rather than grams.

A solute is part of the solution, so its mass can never be more than the whole. If your solute value is larger than the solution total the calculation would exceed 100 percent, which is physically impossible, so the tool flags it instead.

Yes. A solute mass of 0 is allowed and returns 0 percent, meaning pure solvent. Negative masses are rejected, and the solution mass must be greater than zero, so a zero solvent with zero solute will not compute.

The percentage is computed at full floating point precision and rounded to nine decimal places, so clean inputs like 10 g in 100 g return an exact 10, while awkward ratios keep enough digits to stay accurate.

No. The calculation runs locally in your browser with JavaScript. Nothing you type is uploaded, logged, or stored, so lab values and formulation figures stay on your device.

Mass percent uses only masses. Molarity divides moles of solute by litres of solution, and molality divides moles of solute by kilograms of solvent. Those need molar mass and volume, while mass percent needs just the two weights.