Mole Calculator

Created by Jack Bowater
Reviewed by Bogna Szyk
Last updated: Nov 27, 2022

Want to know how to calculate moles? Need a grams to moles calculator, or even a moles to grams calculator? Well then you've come to the right place. With our moles to grams converter, you can seamlessly convert between mass, molecular weight and moles. Chemistry just became that little bit easier! Impress your friends with your astounding ability to find how many moles of a substance you have at a kilogram, ounce, or even tonne scale! (Also useful for any serious industrial applications, for all you chemical engineers out there.)

While we're on the topic of chemistry, we have a number of other calculators what you might find useful. Why not check out our molarity calculator or our percent yield calculator.

What is a mole?

A mole is small, subterranean mammal belonging to the family Talpidae. Just kidding - we're sure you've never heard that joke before. A mole is how chemists define an amount of substance, useful when dealing with many different molecules reacting at once (i.e. any reaction). The official International System of Units definition is that a mole is the amount of a chemical substance that contains exactly 6.02214076×1023 (Avogadro's constant) atoms, molecules, ions or electrons (constitutive particles), as of 20th May 2019. Prior to that, a mole was defined as the number of atoms in 12 grams of carbon-12 (an isotope of carbon). Turns out that memorising that definition for my GCSE chemistry exam was pointless. Shame.

So why do chemists use moles, and why do you need a mole calculator? Well, as we said above, it provides a useful metric when dealing with reactions. Maybe an example would explain it best. Lets say you want to neutralise 10 g of hydrochloric acid (HCl in water) with some sodium hydroxide (NaOH). Now, you want the resulting solution to be perfectly neutral, so you don't want to add too much or to little NaOH, making it too basic or acidic respectively. It is therefore useful to find out exactly how many molecules of HCl are in the solution. This is where moles come in handy. To know how to calculate moles, the equation is:

mole = mass / molecular weight

If you wanted to find the concentration of the hydrochloric acid, you could use our concentration calculator.

How to calculate moles - moles to grams converter

Let's do a quick example to help explain how to convert from moles to grams, or grams to moles. We know we have 10 g of HCl, and it has a molecular weight of 36.5 g / mol. Lets plug these numbers into the above equation:

mole = 10 / 36.5 = 0.27 moles = 1.626×10^23 molecules of HCl

We can work out the number of molecules by timesing the moles by Avogadro's constant above. Now we know the amount of molecules of HCl we have, and, since the reaction is 1:1, we need the exact same number of molecules of NaOH to neutralise it. As we need to find the mass of NaOH to add, lets quickly rearrange the equation:

mole = mass / molecular weight (mulitply both sides by molecular weight)

mole * molecular weight = mass (rearrange the equation)

mass = molecular weight * mole

As 1.626×1023 molecules of NaOH is also equal to 0.27 moles, and we know that the molecular weight of NaOH is 40, we can use these numbers to get:

mass = 40 * 0.27 = 10.8 g

So we now know we need 10.8 g of NaOH to exactly neutralise our amount of hydrochloric acid.

We hope this grams to moles calculator (or moles to grams calculator) will help you with your chemical calculations! You may also find our titration calculator of use to you.


What is a mole?

1 mole is the amount of a substance that contains exactly 6.022×1023 of something. While this something could be anything, because it is such a large number it is usually reserved for atoms, molecules, electrons, and ions.

How to find molar mass?

  1. Find the chemical formula for the compound in question.
  2. Grab a periodic table.
  3. Look up the atomic mass of each atom.
  4. Add together the atomic mass of every atom.
  5. The result is the molar mass of your substance.

How to find moles?

  1. Measure the weight of your substance.
  2. Use a periodic table to find its atomic or molecular mass.
  3. Divide the weight by the atomic or molecular mass.
  4. Check your results with Omni Calculator.

How to convert grams to moles?

  1. Find a periodic table.
  2. Calculate the atomic or molecular mass of your substance.
  3. Divide the weight by the atomic or molecular mass.
  4. Use Omni Calculator to verify your answer.

How many grams in a mole?

The amount of grams in a mole depends on the substance you have. To work it out, find the atomic or molecular mass of your substance and multiply it by the number of moles you have. For one mole, the atomic or molecular mass will be the same as the weight.

How many atoms in a mole?

There are 6.02214076×1023 atoms in a mole. It is derived from the amount of atoms in 12 g of the isotope carbon-12.

Jack Bowater
Molecular weight
g / mol
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