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Science Calculators

Percent Composition Calculator

Verified formula Updated Jun 2026 Private — runs on your device

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g/mol
g/mol
Verified formula Private

Percent composition

88.89%

For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.

How to use the Percent Composition Calculator

The Percent Composition Calculator works out your percent composition in an instant. Enter mass of element in compound and molar mass of compound and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.

  1. Enter the mass of element in compound.
  2. Enter the molar mass of compound.
  3. Read off your percent composition — the calculator updates automatically, with no button to press.

Formula

The Percent Composition Calculator uses the formula:

Percent composition = Mass of element in compound ÷ Molar mass of compound × 100

Worked example

For example, with mass of element in compound of 16 g/mol and molar mass of compound of 18 g/mol, the percent composition is 88.89%.

Inputs used
Mass of element in compound 16 g/mol
Molar mass of compound 18 g/mol
Results
Percent composition 88.89%

Results are estimates for educational use, not professional advice.

Frequently asked questions

Divide the element's total mass in the compound by the compound's molar mass and multiply by 100. Oxygen in water is 16 ÷ 18 × 100 ≈ 88.9%.

It is the share of a compound's mass contributed by each element, useful for analysing formulas and purity.

Use the element's total mass in the formula. For example, hydrogen in water is 2 × 1 = 2 g/mol.

Yes. Adding the percent composition of every element in a compound should total 100%.

Enter the mass of element in compound. Enter the molar mass of compound. Read off your percent composition — the calculator updates automatically, with no button to press.

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