Molar Mass Calculator

Type a chemical formula to get its molar mass in g/mol, the count and mass percent of each element and the empirical formula. Use it when weighing reagents for a solution or solving chemistry problems.

How to use

1. Type a formula such as H2O, Ca(OH)2 or CuSO4·5H2O in "Chemical formula", or press one of the "Common compounds".
2. The "Molar mass", the "Formula (Hill order)" and the "Empirical formula" appear at once.
3. The "Composition by element" table lists the count, atomic weight and mass percent of each element.
4. Under "Moles ↔ mass", enter an amount or a mass to convert it to the other.

How it works

• The molar mass is the sum of atomic weight × number of atoms over all elements. Atomic weights are the IUPAC CIAAW abridged standard atomic weights (2024).
• Case matters: Co is cobalt and CO is carbon monoxide. Brackets ( ) [ ] and hydrate dots (· or .) work, and charges are ignored.
• Radioactive elements without a standard atomic weight use the mass number of their most stable isotope, and the page says so. A wrong symbol is reported with its character position.

Questions and answers

What is the molar mass of water (H2O)?

Hydrogen 1.0080 × 2 + oxygen 15.999 = 18.015 g/mol.

Are molecular weight and molar mass the same?

They have the same number but different units. Molecular weight is a relative value with no unit; molar mass is the mass of one mole, written in g/mol.

How do I calculate the molar mass of a hydrate?

Write the water molecules after a dot, as in CuSO4·5H2O, and the water of crystallisation is included. A full stop (.) can be used instead of ·.

How is mass percent calculated?

Divide the atomic weight × count of the element by the molar mass and multiply by 100. For oxygen in water: 15.999 ÷ 18.015 × 100 ≈ 88.8%.