The molar mass of a substance is the sum of the atomic masses of the atoms in its formula: water, H₂O, is 2 · 1.008 + 15.999 = 18.015 g/mol. The calculator reads the formula, counts the atoms through brackets and hydrate dots, and adds up the standard atomic weights from IUPAC’s Commission on Isotopic Abundances and Atomic Weights, the same values as on the periodic table. With a mass in grams it also gives the amount of substance, n = m / M.
Molar mass calculator
Type a chemical formula and see its molar mass, with each element's share of it, and turn grams into moles.
Start every symbol with a capital letter: Co is cobalt, CO is carbon monoxide. Brackets, a hydrate dot (CuSO4·5H2O, or * or .) and a charge (SO4^2-) are understood.
Try:
Molar mass
M(H₂O) = 18.015 g/mol
Given to 3 decimals: a sum is no more precise than the least precise atomic weight in it.
| Element | Atoms | Atomic mass (g/mol) | Mass (g/mol) | Mass % |
|---|---|---|---|---|
| H Hydrogen | 2 | 1.0080 | 2.0160 | 11.2 |
| O Oxygen | 1 | 15.999 | 15.999 | 88.8 |
| Total | 18.015 | 100.0 |
Last reviewed October 19, 2026 ·How pages are reviewed
Related calculators
- Scientific calculatorType or tap an expression — the result updates as you type, and your calculations stay in the link.
- Proportion calculatorSolve a is to b as c is to x. Enter any three numbers to find the fourth.
- Unit converterPick a quantity, type a value and choose the units. Every factor is exact and comes with its source.
- Percentage calculatorThree everyday percentage questions in one place — pick the one you need.
- Chemical equation balancerType a reaction and see it balanced, with the atoms of every element counted on both sides.
- Derivative calculatorType a function and see its derivative written the way you would write it by hand — and what it comes to at a point.
The formula behind this
Put this calculator on your site
Copy the code into your page where the calculator should appear. It loads from lovetocalc.com, so it stays current on its own — all we ask is that the credit line comes with it.