About the Mole Calculator
Mole Calculator converts between the mass of a substance in grams, the amount in moles and the number of particles (atoms, molecules or formula units). Type a chemical formula such as H2O or C6H12O6, or enter a molar mass directly, then enter the mass, the moles or the number of particles. The page finds the molar mass from standard atomic weights, uses Avogadro's number of 6.02214076 × 10²³ per mole and shows all three quantities at once. It is a quick helper for chemistry homework and lab preparation.
Updated October 2026
How to use the Mole Calculator
- 1Type the chemical formula, or enter the molar mass.
- 2Choose whether you know the mass, the moles or the particles.
- 3Enter the value; for large particle counts use e notation such as 1.2e24.
- 4Read the mass, moles and particles.
- 5Copy the answer.
The mole as a counting unit
Atoms are far too small to count one by one, so chemists count them in huge groups called moles, in the same way you buy eggs by the dozen. One mole of anything has 6.022 × 10²³ items. The molar mass links the world of grams, which you can weigh, to the world of particles, which you cannot see.
Three conversions in one
Almost every chemistry calculation moves between three quantities. The page does all the arithmetic and shows each of them, so you can use it as a check on your own working.
- moles = grams ÷ molar mass
- grams = moles × molar mass
- particles = moles × 6.022 × 10²³
Using it in a larger problem
To work out how much product a reaction gives, convert the mass of the limiting reactant to moles, use the ratio from the balanced equation and convert back to grams. The Chemical Equation Balancer gives the ratio, and the Percent Yield Calculator compares what you got with what you expected.
Related tools
Find the molar mass of any compound with the Molecular Weight Calculator, balance the equation with the Chemical Equation Balancer and prepare solutions with the Molarity Calculator. The Dilution Calculator helps with the next step.
Features
- Molar mass from any formula, with brackets and hydrates
- Grams, moles and particles together
- Avogadro's number built in
- Direct molar mass entry
- Scientific notation for very large or small values
- Private: nothing is uploaded
Frequently asked questions
What is a mole?
The amount of substance that contains 6.02214076 × 10²³ particles, called Avogadro's number. One mole of a substance has a mass in grams equal to its relative formula mass.
How do I convert grams to moles?
Divide the mass in grams by the molar mass in g/mol. For 18 g of water (18.015 g/mol) that is about 1.0 mol.
How do I convert moles to grams?
Multiply the moles by the molar mass.
How do I find the number of molecules?
Multiply the moles by Avogadro's number, 6.022 × 10²³.
How is the molar mass found?
By adding the standard atomic weights of every atom in the formula. Water, H2O, is 2 × 1.008 + 15.999 = 18.015 g/mol.
What are formula units?
Ionic compounds such as NaCl do not form molecules, so chemists count formula units instead. The mole works the same way.
Why are my numbers slightly different from my textbook?
Textbooks round atomic weights differently. Use the same set of values throughout a calculation.
How many significant figures should I report?
Match the least precise measurement you used. If a mass is given to three significant figures, round the answer to three, even though the page shows more digits.
Can I convert moles of gas to litres?
At standard temperature and pressure (0 °C and 1 atm) one mole of an ideal gas takes up 22.4 litres, and at room temperature about 24 litres. For other conditions use the ideal gas law.
Is anything stored?
No. The calculation runs in your browser.