Percent Composition of Water (H₂O)
Water (H₂O) has a molar mass of 18.015 g/mol: 11.19% hydrogen and 88.81% oxygen by mass.
How to use this tool
- Enter h contribution, c contribution, n contribution, o contribution and other elements contribution in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your total molar mass and the full breakdown beneath it.
Calculate the percent composition of water by entering the hydrogen and oxygen contributions.
Frequently asked questions
- What does percent composition mean?
- It tells you what fraction (by mass) of a compound is made of each element. For example, water is about 11.2% hydrogen and 88.8% oxygen by mass.
- How do I find the element contribution?
- Multiply the element's atomic mass (from the periodic table) by the number of atoms of that element in the chemical formula.