Mass Percent Calculator

Concentration by Mass

Mass percent (often denoted as %w/w or weight/weight percent) is one of the simplest and most robust ways to express the concentration of a mixture. Because it is based entirely on mass, it is completely immune to temperature changes, unlike volume-based measurements.

Mass percent simply tells you how many grams of solute are present in exactly 100 grams of the total solution.

For instance, a $5\%$ by mass solution of NaCl means that for every $100 \, \text{grams}$ of the entire salt-water mixture, exactly $5 \, \text{grams}$ of it is pure NaCl, and the remaining $95 \, \text{grams}$ is water.

Calculating Mass Percent

To calculate mass percent, you divide the mass of the solute (the substance being dissolved) by the total mass of the entire solution (solute + solvent), and then multiply by 100.

The Formula

Example Calculation

Imagine you dissolve $20 \, \text{grams}$ of sugar into $180 \, \text{grams}$ of coffee. What is the mass percent of the sugar?

1. Calculate Total Solution Mass: $20 \, \text{g} \, \text{(sugar)} + 180 \, \text{g} \, \text{(coffee)} = \mathbf{200 \, \text{g} \, \text{total}}$.
2. Divide Solute by Total: $20 / 200 = \mathbf{0.10}$.
3. Multiply by 100: $0.10 \cdot 100 = \mathbf{10\%}$.

The resulting beverage is $10\%$ sugar by mass.