Mole Calculator

Use the mole calculator below to find the quantity of a substance using a chemical formula or known molar mass.

grams
g/mol
grams

Quantity:

 
moles

Molar Mass

 
g/mol


What is a Mole?

The mole, abbreviated mol, is the SI base unit to measure the amount or quantity of substance.[1]

It’s used as a standard measurement for a very large quantity of very small units of matter. One mole is equal to 6.02214076 × 1023 elementary entities, such as atoms, molecules, or ions.

This numerical value is known as the Avogadro constant. Because it’s such a large number, scientific notation is almost always used to represent it.

How to Calculate Moles

Since the mole is a measure of quantity, all substances have the same number of atoms, molecules, and other particles in one mole of substance.

You might be wondering how you can calculate the number of moles given a mass, volume, or amount of substance. Follow along, and we’ll show you how to convert mass to moles in just a few steps. Below we’ll also cover how to convert volume and molecules to moles as well.

infographic showing six different mole conversion formulas

Step One: Calculate Molar Mass

The first step to finding the amount of moles of substance is to determine the molar mass of the chemical formula. Molar mass is often expressed as g/mol.

You can calculate molar mass by finding the number of atoms in the molecular formula, then adding the atomic mass of each element together to find the molecular weight. The atomic mass can be found on the periodic table.

For example, let’s find the molar mass of water (H2O).

H2O is composed of two parts hydrogen (H) and one part oxygen (O).

The atomic mass of hydrogen is 1.00794 and oxygen is 15.9994. Since there are two hydrogen atoms per molecule and one oxygen atom, the formula should look like this:

molar mass = 1.00794 + 1.00794 + 15.9994

Therefore, the molar mass of H2O is 18.01528.

Of course, if you don’t have the molar mass handy and want to skip this step, you can use our molar mass calculator to easily calculate the molecular weight of a substance.

Step Two: Convert Mass to Moles

Now that you’re armed with the molar mass of the substance, you can calculate the quantity in moles using the total mass in grams.

Mass to Moles Formula

Calculate moles of substance using the following formula:

n = mM

The quantity of substance n in moles is equal to the mass m in grams divided by the molar mass M in g/mol.

For example, let’s calculate the quantity in moles of 25 grams of oxygen gas (O2). Oxygen has a molar mass of 31.9988 g/mol.

n = 2531.9988
n = 0.78128 mol

Therefore, 25 grams of oxygen is 0.78128 moles.

You can use the calculator above to more easily calculate this or even our grams to moles calculator to quickly convert grams to moles and moles back to mass.

How to Convert Gas Volume to Moles

The process for converting the volume of ideal gas to moles is a little different than mass. You’ll still use a formula, but you do not need the molar mass of the substance for the conversion.

mol = volume [L]22.4

The quantity of substance in moles is equal to the volume of in liters of ideal gas divided by 22.4 L/mol.

You can also use our liters to moles calculator for this conversion.

How to Convert Molecules to Moles

The formula for converting molecules to moles is a little different than mass and volume.

mol = molecules6.02214076 × 1023

The quantity of substance in moles is equal to the number of molecules divided by the Avogadro constant (6.02214076 × 1023).

Our atoms to moles calculator also easily converts atoms or molecules to moles.

References

  1. International Bureau of Weights and Measures, SI base unit: mole (mol), https://www.bipm.org/en/si-base-units/mole