Molar Mass Calculator
Type a chemical formula and this calculator adds up the atomic mass of every atom in it to find the molar mass, in grams per mole.
| H × 2 | 2 atoms |
|---|---|
| O × 1 | 1 atom |
Use capital letters for element symbols and brackets for groups, e.g. Mg(NO3)2 for magnesium nitrate.
Why molar mass matters
Molar mass converts between the mass of a substance you can weigh and the number of particles (atoms, ions or molecules) it contains. One mole is 6.022 × 10²³ particles — Avogadro's number — and its mass in grams is the molar mass. That lets you measure out exact ratios of reactants by mass, which is how real chemical equations are scaled up from the lab bench to industry.
How to calculate molar mass
Read the formula one element at a time. The small number after a symbol tells you how many of those atoms there are, and a number after a bracket multiplies everything inside it. Look up each element’s relative atomic mass on the periodic table, multiply it by the number of atoms, and add the results. The total is the molar mass in g/mol.
The same number is called the relative formula mass (Mr) in GCSE chemistry, where it has no units. Once you have it, moles = mass ÷ molar mass: 49 g of sulfuric acid is 49 ÷ 98.09 ≈ 0.5 mol.
Worked example: sulfuric acid, H₂SO₄
- Hydrogen: 2 × 1.008 = 2.02
- Sulfur: 1 × 32.07 = 32.07
- Oxygen: 4 × 16.00 = 64.00
- Total: 98.09 g/mol
See every element's atomic mass up close, with its protons, neutrons and electrons, in the periodic table or by building it yourself in the Atom Builder below.
Preguntas frecuentes
How do you find the molar mass of a compound?
Add up the atomic mass of every atom in the formula. For water, H₂O, that is 2 × 1.008 (hydrogen) + 1 × 16.00 (oxygen) = 18.02 g/mol.
What is molar mass measured in?
Grams per mole (g/mol). One mole of a substance always has a mass in grams equal to its molar mass.
Is molar mass the same as molecular weight?
Yes — molar mass and molecular weight (or formula weight for ionic compounds) are the same number, in g/mol.
How do you write a formula with a group in brackets?
Multiply everything inside the brackets by the number after them. Ca(OH)₂ means one calcium plus 2 × (one oxygen + one hydrogen).
