What is a mole in chemistry?

A mole is the SI unit for amount of substance. One mole contains exactly 6.022 x 10^23 particles (Avogadro's number). The mass of one mole of a substance in grams is its molar mass, which is numerically the same as its molecular weight in atomic mass units.

What is the moles formula?

Moles (n) equals mass in grams (m) divided by molar mass in grams per mole (M): n = m / M. Rearranged: mass equals moles times molar mass (m = n x M), and molar mass equals mass divided by moles (M = m / n).

How many moles are in 18 grams of water?

Water (H2O) has a molar mass of 18.02 g/mol. Dividing 18 grams by 18.02 g/mol gives approximately 1.00 mole. This matches the default worked example in the calculator.

Moles Calculator

This moles calculator converts between mass, moles, and molar mass using the fundamental relationship n = m / M, where n is the number of moles, m is the mass in grams, and M is the molar mass in grams per mole. The mole is the chemist's counting unit: one mole contains 6.022 x 10^23 particles, and it is the unit every balanced chemical equation is written in. Because you cannot count individual molecules directly but you can weigh a sample on a balance, converting between mass and moles is the single most common calculation in chemistry. It is the starting point for working out reacting quantities, theoretical yields, and solution concentrations. You pick which quantity to solve for, enter the other two, and the result appears immediately. To find moles, the calculator divides mass by molar mass. To find mass, it multiplies moles by molar mass. To find molar mass, it divides mass by moles. If you do not know the molar mass of your compound, use the molar mass calculator with the chemical formula first and then enter the result here. Mass is always in grams, and molar mass is always in grams per mole. The default example is 18 g of water, which has a molar mass of 18.02 g/mol, giving just under 1.00 mol. This tool is for chemistry students, lab technicians preparing solutions, and anyone doing stoichiometry calculations. Results are mathematical and assume pure substances; real samples may contain impurities.

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Solve for

Mass (g)

Molar mass (g/mol)

g/mol

Moles (mol)

mol

1.00 mol

moles

Mass18.00 g

Molar mass18.02 g/mol

Moles1.00 mol

Mass in grams, molar mass in grams per mole. Use the Molar Mass Calculator to find the molar mass of your compound from its chemical formula.

How it works

The three quantities are linked by n = m / M. To find moles (n): divide mass (m) by molar mass (M). To find mass (m): multiply moles (n) by molar mass (M). To find molar mass (M): divide mass (m) by moles (n). The selected variable's input row is hidden so you only enter the two known values. Division by zero or negative values is caught and a prompt is shown instead of a nonsensical result.

Worked example

You have 18 g of water (H2O). The molar mass of water is 18.02 g/mol. Moles = 18 / 18.02 = 1.00 mol. This matches the default values pre-filled in the calculator above. If you had 36 g of water, you would have 2.00 mol; if you had 9 g, you would have 0.50 mol.

Related calculators

Molar Mass Calculator: find molar mass from a chemical formula such as H2O or C6H12O6.
Molarity Calculator: solve M=n/V for solution concentration, moles, or volume.
Dilution Calculator: work out stock and diluent volumes using C1V1=C2V2.
Ideal Gas Law Calculator: use moles in the ideal gas law PV=nRT.

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