Percent Composition Calculator (Mass Percent)
Enter a formula and an element to get its mass percent and how much is in your sample.
Your numbers
Your results
Mass percent of the element
Mass percent of the element
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Mass of the element in your sample (g)
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Percent composition
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Molar mass of the compound (g/mol)
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Atomic weight of the element
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Percent Composition Calculator (Mass Percent) by TheCalcTools
How the Percent Composition Calculator (Mass Percent) works
Mass percent of an element = (number of its atoms × atomic weight) ÷ molar mass of the compound × 100. The full composition is listed for every element.
Multiply the mass percent by a sample mass to find how much of that element the sample contains, for example the iron in iron ore.
The formula
Mass % = n × A ÷ M × 100
Worked example
Using the default values shown in the calculator:
| Chemical formula | Fe2O3 |
|---|---|
| Element symbol | Fe |
| Sample mass (g) | 100 |
- Fe2O3 is 159.687 g/mol: Fe 69.94%, O 30.06%.
- So iron is 69.94% of the mass, and 100 g of Fe2O3 contains 69.94 g of iron.
Result:
| Mass percent of the element | 69.94% |
|---|---|
| Mass of the element in your sample (g) | 69.943 |
| Percent composition | Fe 69.94%, O 30.06% |
| Molar mass of the compound (g/mol) | 159.687 |
| Atomic weight of the element | 55.845 |
Frequently asked questions
Do the percentages add to 100?
Yes, apart from rounding in the last digit.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.