Mass Percent Calculator (Percent Composition)

Mass percent of each element in a formula, or the mass percent of a solute in a solution.

Mass percent of an element = (atoms × atomic mass ÷ molar mass) × 100. In glucose, C₆H₁₂O₆ (180.16 g/mol), carbon is 6 × 12.011 ÷ 180.16 = 40.0%. For a solution, % w/w = solute mass ÷ (solute + solvent mass) × 100.

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How to use it

Choose a formula's percent composition or a solution's mass percent.
Type the formula (hydrates and brackets work), or enter solute and solvent masses.
Read each element's mass percent or the solution's % w/w.

What you enter

Chemical formula
or masses of solute and solvent

What you get

Molar mass
Mass percent of each element
% w/w of a solution

Formula

% element = (n × A / M) × 100 | % w/w = m(solute) / m(solution) × 100

Worked example: sulfuric acid

Input: H2SO4

Result: H 2.06%, S 32.69%, O 65.25%

Oxygen makes up nearly two-thirds of the mass.

Questions

How do you calculate mass percent of an element?

Multiply the atomic mass by the number of atoms in the formula, divide by the molar mass of the compound and multiply by 100.

How do you calculate mass percent of a solution?

Divide the mass of solute by the total mass of the solution (solute + solvent) and multiply by 100. 15 g salt in 85 g water is 15%.

Is mass percent the same as w/v percent?

No. % w/w uses the solution's mass; % w/v uses grams per 100 mL of solution. Use the percent solution calculator for w/v.

Do the percentages add up to 100?

Yes, the element percentages in a compound always total 100%, which is a quick check on your working.

More Chemistry

All free tools · By Dr. Zubair Khalid, DVM, MS, PhD.