Mass Percent Calculator
What the mass percent calculator does
The mass percent calculator expresses the concentration of a solution as the mass of solute divided by the total mass of the solution, times 100. Enter the mass of the dissolved substance in grams and the total mass of the solution in grams, press Calculate, and the result is the mass percent, written as % w/w or % (m/m).
The formula
mass % = (mass of solute ÷ mass of solution) × 100
The denominator is the whole solution, solute plus solvent, not the solvent alone. Dissolving 10 g of salt in 90 g of water gives a solution mass of 100 g and a concentration of 10%, not 11.1%.
Worked examples
| Solute | Solvent | Solution mass | Mass % |
|---|---|---|---|
| 5 g NaCl | 95 g water | 100 g | 5.00% |
| 25 g sugar | 75 g water | 100 g | 25.0% |
| 3.5 g salt | 96.5 g water | 100 g | 3.50% (seawater) |
| 12 g KOH | 188 g water | 200 g | 6.00% |
| 0.9 g NaCl | 99.1 g water | 100 g | 0.90% (normal saline) |
Working backwards
The formula rearranges easily. To prepare 250 g of a 4% glucose solution you need 0.04 × 250 = 10 g of glucose and 240 g of water. To find how much solute is in 500 g of a 12% solution: 0.12 × 500 = 60 g. If you know the solute mass and the target percentage, solution mass = solute ÷ (percent ÷ 100): 15 g of solute at 6% needs a 250 g solution, so add 235 g of solvent.
Mass percent, mass/volume and molarity
| Unit | Definition | Typical use |
|---|---|---|
| % w/w (this calculator) | g solute per 100 g solution | Reagent labels, industrial chemistry, food |
| % w/v | g solute per 100 mL solution | Clinical and pharmacy solutions |
| % v/v | mL solute per 100 mL solution | Alcohol and liquid mixtures |
| Molarity (M) | mol solute per litre of solution | Laboratory stoichiometry |
Mass percent has one advantage: it does not change with temperature, because masses do not expand. Converting to molarity needs the solution density and the solute’s molar mass. For 37% hydrochloric acid with density 1.18 g/mL: 1 L weighs 1,180 g and contains 0.37 × 1,180 = 437 g HCl, which at 36.46 g/mol is 12.0 mol, so the acid is 12.0 M. The molarity calculator and molar mass calculator handle those steps.
Mass percent of an element in a compound
The same ratio describes composition. In water, hydrogen is 2 × 1.008 ÷ 18.015 = 11.2% by mass and oxygen 88.8%. In calcium carbonate, calcium is 40.08 ÷ 100.09 = 40.0%. Enter the element’s mass contribution as the solute and the compound’s molar mass as the solution to use this calculator for that purpose, or use the percent composition calculator, which does the whole formula at once.
Common mistakes
- Dividing by the solvent instead of the solution. Always add the solute mass to the solvent mass for the denominator.
- Using volume for water. 100 mL of water is 100 g at room temperature, but other solvents are not 1 g/mL; ethanol is 0.789 g/mL.
- Weighing a hydrate as if anhydrous. 10 g of CuSO₄·5H₂O contains only 6.4 g of CuSO₄.
- Mixing % w/w and % w/v. A 10% w/v sugar solution is 10 g in 100 mL, which weighs about 104 g, so it is 9.6% w/w.
Related tools
The dilution calculator finds how much solvent to add to reach a lower percentage. The solution concentration calculator switches between units, and the freezing point depression and boiling point elevation calculators use concentration to predict physical changes.
External references
Frequently asked questions
Is mass percent the same as weight percent?
Yes. Weight percent, wt%, % w/w and mass fraction × 100 all mean the same thing.
Can the result exceed 100%?
No. If it does, the solution mass was entered as the solvent mass. Add the solute mass to it.
How do I convert mass percent to parts per million?
Multiply by 10,000. A 0.05% solution is 500 ppm.
Does temperature change mass percent?
No. Mass does not vary with temperature, which is why this unit is preferred for reagents that are stored and shipped.
What is the mass percent of a saturated salt solution?
Sodium chloride saturates at about 26.3% w/w at 20 °C, equal to 36 g of salt per 100 g of water.