How to use the percent composition by mass calculator
Find mass percent of one element in a compound. Enter chemical formula, element symbol, atoms of element in formula in the fields above; the molar mass, element mass percent, remaining mass percent are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- f — Chemical formula
- el — Element symbol
- k — Atoms of element in formula
Worked example
With chemical formula = Fe2O3, element symbol = Fe, atoms of element in formula = 2, the calculator gives molar mass ≈ 159.687 g/mol; element mass percent ≈ 69.94308 %; remaining mass percent ≈ 30.05692 %.
Frequently asked questions
What is the formula for the percent composition by mass calculation?
Molar mass (g/mol) = molmass(f). Element mass percent (%) = 100 × k × atomicMasses[el] / [Molar mass]. Remaining mass percent (%) = 100-[Element mass percent]. Here f is chemical formula, el is element symbol, k is atoms of element in formula.
What inputs do I need for the percent composition by mass calculator?
You need chemical formula, element symbol, atoms of element in formula. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.