Percent Composition Calculator
Mass share of each element, totalling exactly 100.
Work out Percent Composition. Mass share of each element, totalling exactly 100. Temperature in kelvin, handled for you.
Case sensitive. Brackets and hydrates supported.
Largest component by mass
O 65.25%
H2SO4 · 98.072 g/mol
Each element's share is its atomic weight times its count, over the total. The percentages total exactly 100 by construction, which makes this a useful check on a formula: if a lab analysis disagrees with these figures by more than the measurement error, the compound is not what the formula says.
How the Percent Composition Calculator works
Each element's share is its atomic weight times its count, over the total. The percentages total exactly 100 by construction, which makes this a check on a proposed formula rather than merely a description of a known one.
Also known as: mass percent calculator · percentage composition by mass · elemental composition calculator · percent by mass calculator
Frequently asked questions
How do I calculate percent composition?
Divide each element's total mass contribution by the compound's molar mass and multiply by 100. Water is 11.19% hydrogen and 88.81% oxygen.
What is it used for?
Verifying a formula against a laboratory analysis. If combustion analysis disagrees with these figures beyond measurement error, the compound is not what the formula claims.
Why does oxygen dominate so many compounds?
Because it is heavy relative to hydrogen and carbon and appears in large numbers. In water two hydrogens contribute barely a ninth of the mass despite being two thirds of the atoms.
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