Percent Composition Calculator
Calculate the percentage by mass of each element in a compound.
About Percent Composition Calculator
Percent composition converts a formula into the mass fractions you would measure by analysis. The defaults give glucose, which is 40.0% carbon, 6.7% hydrogen and 53.3% oxygen. Comparing calculated percent composition with elemental analysis is the standard way to confirm a proposed formula.
Formula
Percent Composition
Element % = (atoms × atomic mass) ÷ molar mass × 100
- percent composition
- Mass share of each element, summing to 100%
Worked example
With the default values below, Percent Composition Calculator returns Percentage of Element 1 of 40.0020%. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Total mass of element 1 in the formulaminimum 0 g/mol
- 72.066 g/mol
- Total mass of element 2 in the formulaminimum 0 g/mol
- 12.096 g/mol
- Total mass of element 3 in the formulaminimum 0 g/mol
- 95.994 g/mol
Results
- Percentage of Element 1
- 40.0020%
- Percentage of Element 2
- 6.7142%
- Percentage of Element 3
- 53.2838%
- Molar Mass of the Compound
- 180.1560 g/mol
- Sum of the Percentages
- 100.000%
Step by step
- 1Values used
- 2Percent Composition
- 3Percentage of Element 1= 40.0020
- 4Percentage of Element 2= 6.7142
- 5Percentage of Element 3= 53.2838
- 6Molar Mass of the Compound= 180.1560 g/mol
- 7Sum of the Percentages= 100.000
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Percent Composition calculated?
Element % = (atoms × atomic mass) ÷ molar mass × 100 Percent composition converts a formula into the mass fractions you would measure by analysis. The defaults give glucose, which is 40.0% carbon, 6.7% hydrogen and 53.3% oxygen.
Why does Percent Composition matter?
Comparing calculated percent composition with elemental analysis is the standard way to confirm a proposed formula.
What values do I need to enter?
This calculator takes 3 inputs: Total mass of element 1 in the formula, Total mass of element 2 in the formula, Total mass of element 3 in the formula. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.