Moles Calculator

1. Enter any two of amount, mass and molar mass.
2. Take the molar mass from the periodic table (grams per mole).
3. Leave the one you want to find blank.
4. Read the result and the number of particles it represents.

Here is what each result means:

A mole is the chemist's way of counting particles. One mole is exactly 6.022 times 10 to the power of 23 particles, a number called Avogadro number. Because atoms and molecules are far too small and numerous to count directly, the mole lets chemists work with amounts they can actually weigh on a balance.

The link between a countable amount and a weighable mass is the molar mass, measured in grams per mole. The molar mass of a substance equals the sum of the atomic masses of its atoms, read from the periodic table. Water, for example, has a molar mass of about 18 grams per mole, so 18 grams of water is one mole.

The central rule is simple: the number of moles equals the mass divided by the molar mass. This single relationship turns a mass you can measure into a number of moles you can use in a chemical equation, which is why it is one of the first and most important calculations in chemistry.

It rearranges one relation to solve for whichever value you leave blank.

1. For the amount, divide the mass by the molar mass.
2. For the mass, multiply the amount by the molar mass.
3. For the molar mass, divide the mass by the amount.

Moles feed into concentration and gas problems; see the molarity calculator and ideal gas law calculator.

You have 18 grams of water, molar mass 18 grams per mole.

Calculation: n = mass / molar mass = 18 / 18 = 1 mole, which contains about 6.022 times 10 to the power of 23 molecules. To find the mass of 2 moles of a substance with molar mass 40, multiply: 2 times 40 is 80 grams.

One relation, rearranged for whatever you need to find.

All three come from moles equals mass over molar mass, so any two of the values give the third. This makes the mole rule the bridge between the mass you weigh in the lab and the number of particles that take part in a reaction.

The molar mass depends on which atoms make up the substance.

To find a molar mass, add up the atomic masses of every atom in the formula. Glucose, with six carbons, twelve hydrogens and six oxygens, comes to about 180 grams per mole, so 180 grams of glucose is one mole.

The Mass

A larger mass of the same substance contains more moles, in direct proportion.

The Molar Mass

A heavier molar mass means fewer moles for the same mass, since each mole weighs more.

The Substance

The same mass of two different substances contains different numbers of moles because their molar masses differ.

Chemistry Homework

Convert between mass and moles for any substance in a problem.

Stoichiometry

Find the moles that react or form, then relate them through a balanced equation.

Laboratory Work

Weigh out the right mass to get a target number of moles.

1. Wrong Molar Mass

Add up the atomic masses of every atom in the formula, including subscripts, from the periodic table.

2. Mass in the Wrong Unit

Use grams. Convert kilograms or milligrams to grams first.

3. Confusing Moles and Molecules

One mole is Avogadro number of particles, about 6.022 times 10 to the power of 23, not a single molecule.

4. Forgetting Subscripts

Water is H2O, so count two hydrogen atoms, not one, when finding its molar mass.

5. Zero Molar Mass or Amount

Solving for moles or molar mass cannot divide by zero.

The relation is exact; only the displayed decimals are rounded, and very large or small results are shown in scientific notation.

A mole is a fixed number of particles, exactly 6.022 times 10 to the power of 23, called Avogadro number. It lets chemists relate a weighable mass to a countable number of atoms or molecules.

Divide the mass in grams by the molar mass in grams per mole. For 18 grams of water with a molar mass of 18, that is 18 divided by 18, which is 1 mole.

Multiply the amount in moles by the molar mass. Leave the mass field blank and enter amount and molar mass, and the calculator solves for it.

Molar mass is the mass of one mole of a substance, in grams per mole. It equals the sum of the atomic masses of all the atoms in the formula, read from the periodic table.

Add up the atomic masses of every atom in the formula, including subscripts. Water, H2O, is about 2 times 1 plus 16, which is 18 grams per mole.

Avogadro number is 6.022 times 10 to the power of 23, the number of particles in one mole. This calculator uses it to report how many particles an amount contains.

Grams for mass and grams per mole for molar mass, giving an amount in moles. Convert other mass units to grams before entering them.

Moles measure the amount of a substance. Molarity measures concentration, the moles of solute per liter of solution. You often find moles first, then use them to work out molarity.

No. The calculation runs in your browser and nothing you enter is stored or sent anywhere, unless you choose Save, which keeps the result only on this device.

• Mole (unit) (Wikipedia).
• Molar mass (Wikipedia).
• Avogadro constant (Wikipedia).