Mass Percent Concentration Calculator
Work out mass percent concentration from solute, solvent and solution masses, find the solute and water needed for a target solution, mix or evaporate solutions, and convert between mass percent and molarity using density and molar mass — all with the working shown.
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Mass Percent Concentration Calculator
How to use
- 1
Choose the calculation
Select the basic concentration, mixing/evaporation, or molarity conversion.
- 2
Enter values and units
Use g for masses, mol/L for molarity, g/mL for density and g/mol for molar mass.
- 3
Check the result and working
See the concentration, solution, solute and solvent masses, the steps, and the cautions.
Features
- Concentration from solute, solvent and solution masses without mixing up the denominator
- Solute and water needed for a target solution
- Concentration after mixing two solutions or adding/evaporating water
- Conversion between mass percent and molarity using density and molar mass
- The working and the solute/solvent/solution breakdown for every calculation
- Runs entirely in your browser; no sign-up and nothing uploaded
Use cases
Science homework
Check brine and solution problems with the denominator made explicit.
Preparing solutions
Find the solute and water masses for a target concentration.
Converting units
Convert between mass percent and molarity using density and molar mass.
Details
Mass percent is the mass of solute divided by the total mass of the solution (solute + solvent), expressed as a percentage: mass percent (%) = solute (g) ÷ solution (g) × 100. Dissolving 10 g of salt in 90 g of water gives 10 ÷ (90+10) × 100 = 10%.
The denominator is the whole solution, not the solvent. Dissolving 20 g of salt in 100 g of water gives 20 ÷ 120 × 100 ≈ 16.7%, not 20%. This confusion is the most common mistake with mass percent.
For a target solution, solute = solution × percent ÷ 100 and solvent = solution − solute. A 200 g batch of 8% brine needs 16 g of salt in 184 g of water. When mixing solutions, the total solute mass is unchanged unless a reaction occurs; when water evaporates, the solute stays behind.
Converting between w (%) and c (mol/L) needs the solution density ρ (g/mL) and the solute molar mass M (g/mol): c = 10wρ/M and w = cM/(10ρ), derived from a 1 L (1000 mL) basis. Density varies with temperature and concentration, so use a measured value when accuracy matters.
FAQ
What is the denominator in mass percent?
The total mass of the solution (solute + solvent). For 10 g of salt in 90 g of water the denominator is 100 g, giving 10%. Using 90 g gives 11.1%, which is wrong.
What percentage is 20 g of salt in 100 g of water?
20 ÷ (100+20) × 100 ≈ 16.7%, not 20%. Note that solubility limits how much can actually dissolve, depending on temperature and the substance.
How do I make 200 g of 8% brine?
Salt = 200 × 8 ÷ 100 = 16 g and water = 200 − 16 = 184 g. Use the "solution mass and target percent" method.
How do I convert between mass percent and molarity?
For 1 L (1000 mL) of solution: mass = 1000 × density, solute = mass × percent ÷ 100, molarity = solute ÷ molar mass. In one line, c = 10wρ/M. Density and molar mass are required.
Is the mixed concentration a simple average?
Only when the masses are equal. In general it is total solute ÷ total solution × 100, so the result moves towards the concentration of the larger mass.
What happens to the concentration when water evaporates?
The solute does not evaporate, so the solute mass stays the same while the solution mass falls, raising the concentration. Once saturation is reached, further evaporation causes crystals to form instead.
Related guide
GuideHow to Calculate Mass Percent Concentration
Mass percent = solute mass ÷ solution mass × 100. Learn why 20 g of salt in 100 g of water is about 16.7% and not 20%, how to prepare 200 g of 8% brine, how mixing and evaporation change the concentration, and how to convert between mass percent and molarity, with a free calculator for checking.
GuideMolarity and Dilution: How to Calculate C = n/V and C₁V₁ = C₂V₂
Calculate molarity from mass and work through a tenfold dilution with units and a diagram. Check final volume, mL versus L, mass percent, pH and calculator inputs.
Related Tools
Moles & Molarity
Calculate molarity from moles and solution volume, or convert mass to moles with a supplied molar mass. View results in mol/L and mmol/L.
Dilution Calculator
Find the required stock volume from stock concentration, target concentration and final solution volume using C₁V₁ = C₂V₂.
Solubility & Recrystallization Calculator
From the solubility per 100 g of water, compute the maximum dissolved amount, the composition of a saturated solution, and the crystals precipitated on cooling or evaporation — with the mass-balance steps shown.
Significant Figures Calculator
Count significant figures, round to a chosen precision, and apply the multiplication/division or addition/subtraction rules. Switch between half-up and JIS Z 8401 half-even rounding; scientific notation is shown alongside.
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Verified: Known values (10 g salt in 90 g water giving 10%, 30 g sugar in 170 g water giving 15%, 200 g of 8% brine needing 16 g salt and 184 g water, 10% 100 g mixed with 5% 200 g giving 6.667%, evaporating 50 g from 200 g of 8% giving 10.67%, 5% NaCl at density 1.033 and M 58.44 giving 0.8838 mol/L, 98% H₂SO₄ giving 18.0 mol/L and 12 mol/L HCl giving 36.5%) plus invalid, over-100% and over-evaporation errors are covered by browser tests
Did you know?
Dissolving 20 g of salt in 100 g of water gives about 16.7%, not 20% (20 ÷ 120 × 100). The denominator is the total solution mass, not the water mass — the most common mistake with mass percent concentration.