‘Formulae' or 'Formulas': What's the Difference?

By Carly Forsaith, updated on January 19, 2023

If you're wondering whether to use 'formulae' or 'formulas' as the plural form of 'formula,' you've come to the right place.

In short, you can use either 'formulae' or 'formulas' since, technically, both are correct.

Difference Between 'Formulae' or 'Formulas'

The thing that makes this one a bit confusing is that 'formulae' doesn't follow the usual pluralization rules. That's why it seems more sense to use 'formulas' since to make a noun plural, you just add -s. That's why 'formulas' is correct.

'Formulae' follows different rules, however. It follows Latin pluralization conventions. It's very common with Latin words to see the ending -ae for plural nouns.

That's why it's okay to use both 'formulae' and 'formulas' when referring to 'formula' in the plural form.

What Does 'Formula' Mean?

The word 'formula' is a noun and is the singular form of 'formulae' or 'formulas.' according to the Cambridge Dictionary, a formula can be one of three things:

  • a standard or accepted way of doing or making something
  • a mathematical rule expressed in a set of numbers and letters:
  • type of milk that can be given to babies instead of milk from their mother

'Formula' is a word borrowed straight from Latin and has been used since the 1630s.

Its verb is 'formulate.'

Pronunciation: How to Pronounce 'Formulae' or 'Formulas'

If you're wondering how to pronounce the words, let me help you out with that. Let's start with 'formulas.'

The International Phonetic Alphabet spells it like this:


And it sounds like this:


As for 'formulae,' it's spelled like this in phonetics:


And it sounds like this:


When to Use 'Formulae' or 'Formulas'

Now it's time to see these words in action. I'll show you a few examples of sentences that use the words. Since they both mean the same thing, I will use them interchangeably in the examples. I'll also use the singular form.

Can you change the baby's diaper while mom prepares the formula?

The recipes are very specific formulas that you need to follow down to a tee.

How many formulae do we need to decode before we get to the answer?

She has been working on these formulas all night.

After much experimenting, I've finally found the perfect formula.

The Bottom Line

So there you have it: 'formulae' and 'formulas' are both correct, so feel free to use whichever one floats your boat.

And if you want to learn about more commonly confused words, why not head to our blog?

We encourage you to share this article on Twitter and Facebook. Just click those two links - you'll see why.

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Written By:
Carly Forsaith
Carly Forsaith is one of the lead freelance writers for WritingTips.org. Carly is a copywriter who has been writing about the English language for over 3 years. Before that, she was a teacher in Thailand, helping people learn English as a second language. She is a total grammar nerd and spends her time spotting language errors on signs and on the internet.

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