Mole Calculator

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 several other calculators that you might find useful. Why not check out our molarity calculator or our percent yield calculator?

A mole is a 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 20^th May 2019. Prior to that, a mole was defined as the number of atoms in 12 grams of carbon-12 (an isotope of carbon). It turns out that memorizing 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. Let's say you want to neutralize 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 too 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.

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, which has a molecular weight of 36.5 g/mol. Let's plug these numbers into the above equation:

mole = 10 / 36.5 = 0.27 moles = 1.626×10²³ molecules of HCl

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

mole = mass / molecular weight (multiply 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 neutralize 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 useful.