Mass Percent Solution Calculator (w/w %)
Calculate the weight/weight percent (w/w %) of a solution: (mass of solute ÷ mass of solution) × 100. Distinct from w/v % which uses volume. For education only.
How to use this tool
- Enter mass of solute and mass of solution in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your mass percent (w/w) and the full breakdown beneath it.
Mass percent (w/w %) = (mass of solute ÷ mass of solution) × 100. For example, 10 g NaCl dissolved in 90 g water gives a 100 g solution that is 10% NaCl by mass.
This differs from w/v % (grams per 100 mL of solution). Use w/w % when working with solid mixtures or very concentrated solutions.
For education only.
Formula
w/w % = (masssolute ÷ masssolution) × 100
Mass of solvent: masssolvent = masssolution − masssolute
How it works
This calculator divides the mass of the dissolved solute by the total mass of the solution (solute + solvent combined) and multiplies by 100 to give the weight/weight percent concentration — the fraction of the solution's mass that is solute.
Both masses must be in the same unit (grams by default). Unlike weight/volume percent (w/v %), this result does not depend on density or temperature, making it suitable for solid–liquid and liquid–liquid mixtures alike. The solute mass cannot exceed the solution mass, as that would imply a negative solvent mass.
Worked example
Worked example: 10 g solute in 100 g solution
- Identify inputs: solute mass = 10.0 g, solution mass = 100.0 g.
- Apply the formula: w/w % = (10.0 ÷ 100.0) × 100 = 10.0 %.
- Calculate solvent mass: 100.0 − 10.0 = 90.0 g.
Mass percent (w/w) = 10.0 %; Mass of solvent = 90.0 g
Common mistakes to avoid
- Dividing solute mass by solvent mass instead of total solution mass -- w/w % = solute divided by (solute + solvent) x 100, not solute divided by solvent x 100.
- Confusing w/w % with w/v % (g per 100 mL) -- the two give different numbers and are not interchangeable without knowing solution density.
- Using different units for solute and solution masses (e.g. grams and kilograms) without converting -- both must be in the same unit before dividing.
Key terms
- Mass percent (w/w %)
- The mass of solute expressed as a percentage of the total solution mass; also called weight percent.
- Solute
- The substance dissolved in a solvent to form a solution; usually the component present in lesser amount.
- Solvent
- The dissolving medium in a solution; the component present in greater amount (e.g., water).
- w/v % (weight/volume percent)
- An alternative concentration unit expressing grams of solute per 100 mL of solution; unlike w/w %, it depends on density.
- Concentration
- A measure of how much solute is present relative to the solution or solvent; expressed in various units including %, mol/L, and mol/kg.
Frequently asked questions
- How is w/w% different from w/v%?
- w/w% uses mass of solution in the denominator; w/v% uses volume (mL). For dilute aqueous solutions (density ≈ 1 g/mL) they are approximately equal, but they diverge at high concentrations.
- Why use mass instead of volume?
- Mass is independent of temperature and pressure, making w/w% more reproducible for concentrated or non-aqueous solutions.