ChemBench

Mass Percentage Calculator

What fraction of the mass is this element?

Element mass divided by total mass

Mass percentage is simply (mass of the element in the formula ÷ total molar mass) × 100 — for water, oxygen makes up about 88.8% of the mass despite being just 1 of the 3 atoms.

Where this matters

Percent composition checks whether a proposed formula matches lab measurements, and is a required step before finding a compound's empirical formula from experimental mass data.

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ChemBench

Mass Percentage Calculator

What fraction of the mass is this element?

Chemical formula

Element symbol

Mass % of O

88.809%

What you entered

Formula: H2OElement: O

1
Mass of O in formula
15.999 × 1= 15.999 g/mol
2
Total molar mass
H2O= 18.015 g/mol
3
Mass percentage
15.999 ÷ 18.015 × 100= 88.8093%

Result

Mass % of O: 88.809%

O makes up 88.809% of the total mass of H2O.

Element mass divided by total mass

Mass percentage is simply (mass of the element in the formula ÷ total molar mass) × 100 — for water, oxygen makes up about 88.8% of the mass despite being just 1 of the 3 atoms.

Where this matters

Percent composition checks whether a proposed formula matches lab measurements, and is a required step before finding a compound's empirical formula from experimental mass data.