Enter a Chemical Formula and the Percent Composition Calculator breaks down exactly how much of each element is in your compound — giving you the Element Percentage, Molar Mass, and Element Mass in Formula. Narrow things down with an optional Element to Analyze, and adjust Decimal Places to control how precise your results appear.
Element Percentage
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Molar Mass
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Element Mass in Formula
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Percent composition is the percentage by mass of each element in a chemical compound. It tells you what fraction of the total mass comes from each type of atom in the molecule.
To calculate percent composition: 1) Find the molar mass of the compound, 2) Find the total mass of each element in the formula, 3) Divide each element's mass by the total molar mass and multiply by 100%.
In water (H2O), hydrogen makes up about 11.19% by mass. This is calculated as: (2 × 1.008) / (2 × 1.008 + 15.999) × 100% = 11.19%.
In sodium bicarbonate (NaHCO₃): Sodium is 27.37%, Hydrogen is 1.20%, Carbon is 14.30%, and Oxygen is 57.14% by mass.
Sugar (C₁₂H₂₂O₁₁) contains about 42.1% carbon by mass, so 100g of sugar would contain approximately 42.1g of carbon.
Yes, the calculator handles complex formulas including parentheses and nested structures like Al₂(SO₄)₃. Enter the formula exactly as written with proper capitalization.
Percent composition helps determine empirical formulas, verify compound purity, calculate how much of a specific element you get from a compound, and compare different compounds containing the same elements.