Percent Composition Calculator
Percent Composition Calculator
Enter a chemical formula and this calculator computes the molar mass, then works out what percentage of that total mass belongs to each element - shown as a breakdown list, a bar chart, and the full calculation steps.
Each element's percentage is its own contribution to the molar mass divided by the compound's total molar mass — in water (H₂O), oxygen alone contributes 15.999 out of the total 18.015 g/mol, working out to 88.81%, with the two hydrogen atoms making up the remaining 11.19%, and every compound's full set of percentages always sums to exactly 100%. This calculator is effectively the reverse process of the Empirical Formula Calculator, which starts from known percentages and works backward to a formula — this one starts from a known formula and works forward to the percentages.
- Percent composition = (mass of that element in the formula ÷ total molar mass) × 100, so in H₂O, oxygen contributes 15.999 out of 18.015 g/mol total, or 88.81%.
- All the percentages in a compound always add up to 100%.
- Percent composition is the reverse process of the Empirical Formula Calculator, which starts from percentages and works back to a formula.
How do I find the percent composition of a compound?
Divide the mass contributed by each element (its count times its atomic mass) by the compound's total molar mass, then multiply by 100.
What is the percent composition of water?
Water (H2O) is about 11.19% hydrogen and 88.81% oxygen by mass.
Percent Composition Calculator
Enter a chemical formula and this calculator computes the molar mass, then works out what percentage of that total mass belongs to each element - shown as a breakdown list, a bar chart, and the full calculation steps.
Each element's percentage is its own contribution to the molar mass divided by the compound's total molar mass — in water (H₂O), oxygen alone contributes 15.999 out of the total 18.015 g/mol, working out to 88.81%, with the two hydrogen atoms making up the remaining 11.19%, and every compound's full set of percentages always sums to exactly 100%. This calculator is effectively the reverse process of the Empirical Formula Calculator, which starts from known percentages and works backward to a formula — this one starts from a known formula and works forward to the percentages.
- Percent composition = (mass of that element in the formula ÷ total molar mass) × 100, so in H₂O, oxygen contributes 15.999 out of 18.015 g/mol total, or 88.81%.
- All the percentages in a compound always add up to 100%.
- Percent composition is the reverse process of the Empirical Formula Calculator, which starts from percentages and works back to a formula.
How do I find the percent composition of a compound?
Divide the mass contributed by each element (its count times its atomic mass) by the compound's total molar mass, then multiply by 100.
What is the percent composition of water?
Water (H2O) is about 11.19% hydrogen and 88.81% oxygen by mass.