％ Mass Percent (w/w) Calculator
Enter the mass of solute and solvent to get the mass percent (%w/w), the concentration on reagent and nutrition labels.
Mass percent (w/w)
10%
Total solution mass
100 g
Mass percent by weight (%w/w) = mass of solute ÷ total mass of solution × 100, where the solution mass is solute + solvent. It's the concentration on nutrition and reagent labels, a 10 g solute in 90 g water is a 10% (w/w) solution. 🔒 In your browser.
How the mass percent (w/w) calculator works
Mass percent by weight is %(w/w) = mass of solute ÷ mass of solution × 100, where the solution's mass is the solute plus the solvent. The tool adds your two masses to get the solution mass and computes the percentage. Any consistent mass unit works, grams in, grams out, since the units cancel in the ratio. Rearranged, the solute mass for a target percent is (percent ÷ 100) × total solution mass, so a 250 g batch of a 4% solution needs 10 g of solute and 240 g of solvent.
Mass percent is distinct from percent composition (the mass fraction of each element within a compound's formula) and from ppm (used for trace amounts). It's the everyday "how concentrated is this solution" figure, a 0.9% saline drip, a 3% hydrogen-peroxide bottle, a 70% isopropyl alcohol.
Frequently asked questions
How do you calculate mass percent?
Mass percent (w/w) = mass of solute ÷ total mass of solution × 100. Dissolve 10 g of salt in 90 g of water and the solution is 10 g ÷ 100 g × 100 = 10% salt by mass.
How do I dilute a mass-percent solution?
Add solvent while keeping the solute mass fixed. Adding 100 g of water to 100 g of a 20% solution (20 g solute) gives 20 g ÷ 200 g × 100 = 10%.
How does mass percent relate to ppm?
1% by mass equals 10,000 ppm, so mass percent × 10,000 gives ppm. A 0.005% solution is 50 ppm, use ppm when the solute is only a trace amount.
What is the difference between %w/w and %w/v?
Mass percent (w/w) is grams of solute per 100 g of solution; weight/volume percent (w/v) is grams per 100 mL of solution. This tool computes w/w; for w/v you'd divide by the solution's volume instead of its mass.
Is mass percent the same as percent composition?
No. Percent composition is the mass fraction of each element inside a compound (from its formula). Mass percent here is the fraction of solute in a solution. Use the percent-composition tool for the former.
How do I make a 10% solution?
Make the solute 10% of the total mass: for 100 g of a 10% solution, use 10 g of solute and 90 g of solvent. Scale as needed, 25 g solute + 225 g solvent is also 10%.
What mass unit should I use?
Any, as long as both masses use the same one, because the units cancel in the ratio. Grams are usual in the lab; the percentage comes out the same whether you use grams or kilograms.