Molar Mass of Water (H₂O)
Water (H₂O) has a molar mass of 18.015 g/mol, calculated from 2 hydrogen atoms (2 × 1.008) plus 1 oxygen atom (15.999).
How to use this tool
- Enter hydrogen (h), carbon (c), nitrogen (n), oxygen (o), sodium (na), chlorine (cl), calcium (ca), iron (fe), sulfur (s), phosphorus (p), potassium (k) and magnesium (mg) in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your molar mass and the full breakdown beneath it.
Water is the most commonly used compound in chemistry labs, and its molar mass of 18.015 g/mol is a fundamental constant for solution preparation.
Frequently asked questions
- Where do atomic masses come from?
- From the IUPAC periodic table. They reflect the natural isotope distribution on Earth, which is why carbon is 12.011 rather than exactly 12.
- What are some common molar masses?
- Water H₂O = 18.015, NaCl = 58.44, glucose C₆H₁₂O₆ = 180.16, CO₂ = 44.01 g/mol.