Calculate mass percent three ways: the concentration of a solution from solute and solvent masses, the percent composition of a compound from its formula (with a full element table), or how much solute you need for a target percentage.
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What do you want to calculate?
g
g
Case matters: Co is cobalt, CO is carbon monoxide. Use · or * for hydrates.
g
Shows grams of each element in this much compound
%
g
Enter your values to see the result.
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How to use the Mass Percent Calculator
Choose a mode: solution, compound composition or target percent.
For a solution, enter the solute mass and the solvent (or solution) mass.
For a compound, type its formula, such as Ca(OH)2 or CuSO4·5H2O.
For a target, enter the percent and total mass you want to make.
Read the result, the steps and the table or chart.
Mass percent formulas
Quantity
Formula
Example
Mass percent of a solution
% = msolute ÷ (msolute + msolvent) × 100
15 g in 85 g water → 15%
Element in a compound
% = n × Ar ÷ M × 100
C in CO₂: 12.011 ÷ 44.009 → 27.29%
Solute for a target %
msolute = % × mtotal ÷ 100
10% of 500 g → 50 g
Mass of element in a sample
m = sample × % ÷ 100
O in 36 g water → 31.97 g
Percent composition of common compounds
Compound
Molar mass (g/mol)
Composition by mass
Water, H₂O
18.015
H 11.19%, O 88.81%
Carbon dioxide, CO₂
44.009
C 27.29%, O 72.71%
Sodium chloride, NaCl
58.44
Na 39.34%, Cl 60.66%
Glucose, C₆H₁₂O₆
180.156
C 40.00%, H 6.71%, O 53.28%
Ammonia, NH₃
17.031
N 82.24%, H 17.76%
Calcium carbonate, CaCO₃
100.086
Ca 40.04%, C 12.00%, O 47.96%
Percent composition is the starting point for working backwards to a formula: use the Empirical Formula Calculator to turn percentages from an analysis into a formula.
Frequently asked questions
What is the mass percent formula?
Mass percent = mass of solute ÷ mass of solution × 100%. The solution mass is solute plus solvent. 15 g of sugar in 85 g of water gives 15 ÷ 100 × 100 = 15% (w/w).
How do I find the percent composition of a compound?
Multiply each element's atomic mass by the number of its atoms, divide by the molar mass of the compound and multiply by 100. In water, H₂O: 2 × 1.008 ÷ 18.015 = 11.19% hydrogen and 15.999 ÷ 18.015 = 88.81% oxygen.
What is the difference between w/w, w/v and v/v percent?
w/w (mass percent) compares masses: grams of solute per 100 g of solution. w/v uses grams per 100 mL of solution, and v/v compares volumes, as in alcohol content. This calculator gives w/w.
Do the mass percentages always add up to 100%?
Yes, for a full compound or solution the parts add up to 100%, apart from small rounding differences in the last decimal place.
How do I make a 10% solution by mass?
For 500 g of a 10% (w/w) solution, weigh 50 g of solute and add 450 g of solvent, so the total is 500 g. Do not add the solute to 500 g of solvent, which would give only 9.09%.
Which atomic masses does the calculator use?
Standard atomic weights from IUPAC (conventional values, e.g. H 1.008, C 12.011, O 15.999, Cl 35.45). Results may differ from textbooks by a few hundredths of a percent depending on the table they use.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.