Mass
g
Molecular weight
g / mol
Moles
mol

# Mole Calculator

By Jack Bowater

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

`mole * mass = molecular weight (divide both sides by mole)`

`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.

Jack Bowater