Molar MassWhat you get
The calculator reads your formula, counts the atoms of each element, and multiplies each count by the element's standard atomic weight from IUPAC. It shows the total in grams per mole, a table of the working that you can compare with your own, and the share of the mass that each element supplies. From the result you can jump to the converter to change grams into moles or to work out the mass for a solution.
Molar mass in one paragraph
One mole of a substance is 6.022 × 1023 of its particles. The molar mass is the mass of that many particles, in grams. It is found by adding up the atomic weights of all the atoms in the formula. Water, H2O, is 2 × 1.0080 + 15.999 = 18.015 g/mol. Chemists use it to weigh out the right number of particles: it is the link between the balance and the chemical equation. The full explanation is on the page what is molar mass?
Common compounds
These pages give the answer with the working written out, notes on the compound and worked examples.
- Hydrogen chloride HCl · 36.46
- Sulphuric acid H2SO4 · 98.07
- Sodium hydroxide NaOH · 40.00
- Ammonia NH3 · 17.03
- Sodium chloride NaCl · 58.44
- Calcium carbonate CaCO3 · 100.09
- Potassium permanganate KMnO4 · 158.03
- Water H2O · 18.02
- Carbon dioxide CO2 · 44.01
- Oxygen O2 · 32.00
- Glucose C6H12O6 · 180.16
- Copper(II) sulphate pentahydrate CuSO4·5H2O · 249.68
Learn the method
- What is molar mass? Start here
- How to calculate molar mass, step by step Method
- The mole and the Avogadro constant Ideas
- Grams to moles and moles to grams Method
- Percentage composition by mass Method
- Empirical and molecular formula Method
Questions people ask
How do I type a formula?
Type it as it is written, with capital letters for the start of each element symbol: H2SO4, Ca(OH)2, Al2(SO4)3. For water of crystallisation use a full stop: CuSO4.5H2O.
Why is my textbook answer slightly different?
Many school books round atomic masses to whole numbers, such as H = 1 and O = 16. This site uses the fuller IUPAC values, such as 1.0080 and 15.999. The compound pages show both answers.
Is molar mass the same as molecular weight?
For everyday calculations, yes: they give the same number. Molar mass is the mass of one mole, in grams per mole.
Does it work for ions and charges?
Leave out the charge. An electron is so light that the mass of an ion is the same as that of its atoms for all practical purposes.
Which values? This site uses the abridged standard atomic weights published by IUPAC (CIAAW), read on 12 November 2026. Your textbook or question paper may round them differently, for example H = 1 and O = 16, so its answer can differ slightly. In an exam, use the values the paper gives.