How to Find Molar Mass
Molar mass is the mass of one mole of a substance in g/mol. Add up the atomic masses of every atom in the formula.
Steps to find molar mass
- Write the formula of the substance, e.g. CO₂.
- Count the atoms of each element (1 C and 2 O).
- Look up each atomic mass on the periodic table (C = 12.011, O = 15.999).
- Multiply and add: 12.011 + 2 × 15.999 = 44.009 g/mol.
Worked examples
| Substance | Working | Molar mass |
|---|---|---|
| H₂O | 2 × 1.008 + 15.999 | 18.015 g/mol |
| NaCl | 22.990 + 35.45 | 58.44 g/mol |
| Ca(OH)₂ | 40.078 + 2 × (15.999 + 1.008) | 74.092 g/mol |
| C₆H₁₂O₆ (glucose) | 6 × 12.011 + 12 × 1.008 + 6 × 15.999 | 180.156 g/mol |
Why molar mass matters
Molar mass converts between grams and moles: moles = mass ÷ molar mass. 36 g of water is 36 ÷ 18.015 ≈ 2.0 mol. You need it for molarity, reaction yields and balancing amounts in a recipe.
Skip the arithmetic with the Molar Mass Calculator, or see milligram conversions in What does mg stand for? and the Molarity Calculator.
Frequently asked questions
How do you find molar mass?
Add up the atomic masses (from the periodic table) of every atom in the formula. The total, in grams per mole (g/mol), is the molar mass.
What is the molar mass formula?
Molar mass = sum of (number of atoms of each element × its atomic mass). For moles, n = mass ÷ molar mass.
How do you find the molar mass of an element?
Read its atomic mass from the periodic table. Carbon is 12.011, so its molar mass is 12.011 g/mol.
What is the molar mass of water?
H₂O = 2 × 1.008 + 15.999 = 18.015 g/mol.
How do you handle brackets in a formula?
Multiply everything inside the bracket by the number after it. In Ca(OH)₂ there is 1 Ca, 2 O and 2 H.
