Grams to moles calculator: mass, moles and particles

To convert grams to moles, divide the mass by the molar mass: n = m ÷ M, with m in grams and M in g/mol. 36.04 g of water (M = 18.02 g/mol) is 36.04 ÷ 18.02 = 2 mol. To go from moles to grams, multiply instead: m = n × M. This grams to moles calculator is our Moles Calculator: it converts between mass and moles, finds a molar mass, and turns moles into a number of particles with the Avogadro constant.

It opens on that water example. Open the full moles calculator over this page to try your own.

Try it

Moles Calculator

Convert between grams, moles and particles

Open the calculatorGo to its page

How to use the grams to moles calculator

1. Under Calculate, choose Mass and moles or Particles.
2. For grams to moles, choose Moles and type the Mass and the Molar mass. Mass can be in mg, g, kg or tonnes.
3. For moles to grams choose Mass, and to work out a molar mass from a mass and an amount, choose Molar mass.
4. In Particles, choose Particles (from moles), Moles (from particles) or From mass (straight from grams to particles).
5. Read the answer and the steps. The extra result gives the number of particles too.
6. To practise, press Random problem in the Practice section.

You need the molar mass of the substance. Multiply each element's relative atomic mass by its number of atoms and add them, or let the molar mass calculator do it from the formula.

Grams to moles formula

n is the amount in moles, m the mass in grams, M the molar mass in g/mol, and N the number of particles. The Avogadro constant, N_A, is exactly 6.02214076 × 10²³ per mole: one mole of anything contains that many particles. The molar mass in g/mol has the same number as the substance's relative formula mass, so water, Mr 18.02, has M = 18.02 g/mol.

Worked examples you can check in the calculator

Example 1: grams of water to moles

n = 36.04 ÷ 18.02 = 2.00 mol. The calculator adds that this is 2 × 6.022 × 10²³ = 1.204 × 10²⁴ molecules.

Example 2: carbon dioxide

How many moles are in 88 g of CO₂? M = 12.011 + 2 × 15.999 = 44.009 g/mol, so n = 88 ÷ 44.009 = 2.00 mol.

Example 3: moles to grams

What mass of sodium chloride (M = 58.44 g/mol) is 0.25 mol? Choose Mass: m = 0.25 × 58.44 = 14.61 g.

Example 4: a small mass

How many moles are in 5.00 g of calcium carbonate, CaCO₃? M = 40.078 + 12.011 + 3 × 15.999 = 100.086 g/mol, so n = 5.00 ÷ 100.086 = 0.0500 mol.

Example 5: grams to molecules

How many molecules are in 1.00 g of water? Choose From mass in the Particles group: N = (1.00 ÷ 18.015) × 6.022 × 10²³ = 3.34 × 10²² molecules. Even a small mass contains a huge number of particles.

Example 6: finding the molar mass

0.100 mol of an acid has a mass of 9.81 g. Choose Molar mass: M = 9.81 ÷ 0.100 = 98.1 g/mol, which matches sulfuric acid, H₂SO₄. Working out a molar mass like this helps identify an unknown substance.

Try one

Common mistakes

• Dividing the wrong way. Moles = mass ÷ molar mass. If you get more moles than grams for anything heavier than hydrogen, check.
• Wrong molar mass. Count every atom, including those in brackets and water of crystallisation.
• Using kg with g/mol. Molar mass is in g/mol, so the mass must be in grams, or choose the unit in the calculator.
• Diatomic elements. Oxygen gas is O₂, so its molar mass is about 32 g/mol, not 16.
• Particles vs atoms. 1 mol of CO₂ has 6.02 × 10²³ molecules but three times as many atoms.

Read next

Chemistry · Moles and quantitiesWhat is a mole in chemistry? Definition, formula, examplesA mole is 6.022 × 10²³ particles: the chemist's counting unit. Learn the mole formula, molar mass and Avogadro's number, with worked examples.