Common Mistakes with the Plural of Formula
If you are unsure whether to write formulas or formulae in your next email or essay, the direct answer is: both are correct, but they are used in different contexts. Formulas is the standard plural for everyday English, while formulae is the traditional Latin plural, still preferred in formal academic and scientific writing. The most common mistake is using one when the other is expected, or mixing them inconsistently in the same piece of writing.
Quick Answer
Use formulas in general writing, business emails, and everyday conversation. Use formulae in formal scientific papers, mathematical contexts, and when following a strict academic style guide. Both are correct, but formulas is far more common in modern English.
Understanding the Two Plurals
The word formula comes from Latin, and like many Latin nouns ending in -a, its original plural was formulae. Over time, English speakers began applying the regular English plural rule (add -s or -es), creating formulas. Today, both forms exist, and your choice depends on tone, audience, and context.
When to Use “Formulas”
Formulas is the default plural in most situations. It is the safe choice for:
- Business reports and emails
- Everyday conversation
- General blog posts and articles
- Informal academic writing
- Instructions and user guides
Using formulas sounds natural and avoids sounding pretentious. If you are writing an email to a colleague about spreadsheet calculations, formulas is the right word.
When to Use “Formulae”
Formulae is the formal, traditional plural. It is appropriate in:
- Scientific research papers
- Mathematical textbooks
- Formal academic writing (theses, dissertations)
- Historical or classical contexts
- Publications that follow a specific style guide (e.g., Chicago Manual of Style)
Using formulae signals a formal tone and attention to traditional usage. However, it can sound overly formal or even outdated in casual contexts.
Comparison Table: Formulas vs. Formulae
| Aspect | Formulas | Formulae |
|---|---|---|
| Origin | English plural rule | Latin plural rule |
| Common usage | Everyday, business, general writing | Formal academic, scientific writing |
| Tone | Neutral, modern | Formal, traditional |
| Frequency | More common in modern English | Less common, but standard in certain fields |
| Example context | “I updated the formulas in the spreadsheet.” | “The mathematical formulae were derived from first principles.” |
| Style guide preference | Preferred by most modern guides | Preferred by some formal academic guides |
Natural Examples
Seeing both forms in real sentences helps you understand the difference in tone and context.
Examples with “Formulas”
- “Please check the formulas in the budget report before sending it to the manager.”
- “The teacher gave us a list of formulas to memorize for the test.”
- “I prefer using simple formulas when calculating discounts.”
- “The software automatically updates the formulas when you add new data.”
Examples with “Formulae”
- “The research paper included several complex formulae for quantum mechanics.”
- “In the appendix, the author listed all the formulae used in the study.”
- “The professor insisted on using the original Latin formulae in the dissertation.”
- “These formulae have been used by mathematicians for centuries.”
Common Mistakes
Even advanced English learners make these errors. Here are the most frequent ones:
Mistake 1: Mixing Both Forms in the Same Document
Using formulas in one paragraph and formulae in another creates inconsistency. Choose one form and stick with it throughout your writing.
Incorrect: “The formulas in chapter one are simple, but the formulae in chapter three are complex.”
Correct: “The formulas in chapter one are simple, but the formulas in chapter three are complex.” (or use formulae for both)
Mistake 2: Using “Formulae” in Casual Contexts
Using formulae in an email to a coworker or in a blog post can sound stiff or unnatural.
Awkward: “I need to update the formulae in the sales forecast.”
Natural: “I need to update the formulas in the sales forecast.”
Mistake 3: Using “Formulas” in Very Formal Academic Writing
Some professors or journal editors expect the traditional Latin plural. Check the style guide or ask your supervisor if you are unsure.
Potentially incorrect: “The formulas derived in this study are presented in Table 1.” (if the journal requires formulae)
Preferred: “The formulae derived in this study are presented in Table 1.”
Mistake 4: Incorrect Pronunciation or Spelling
Formulae is pronounced /ˈfɔːrmjʊliː/ (for-myoo-lee). Some learners misspell it as formulaes or formuli, which are always wrong.
Better Alternatives and When to Use Them
If you are unsure which plural to use, consider these alternatives based on your context:
- For general writing: Always use formulas. It is safe, modern, and widely accepted.
- For formal academic writing: Use formulae if your field or style guide prefers it. If in doubt, check recent papers in your field.
- For mixed audiences: Use formulas. Most readers will not notice or care, and it avoids sounding overly formal.
- For consistency: If you are writing a document that uses other Latin plurals (e.g., criteria, phenomena), consider using formulae to match the tone.
Mini Practice: Test Your Understanding
Choose the correct plural for each sentence. Answers are below.
- The chemistry textbook listed all the important ______ for the exam.
a) formulas b) formulae c) both are acceptable - In his email to the team, he mentioned the ______ for calculating overtime pay.
a) formulas b) formulae c) both are acceptable - The doctoral thesis included a chapter on the historical ______ used by ancient astronomers.
a) formulas b) formulae c) both are acceptable - Please double-check the ______ in the spreadsheet before the meeting.
a) formulas b) formulae c) both are acceptable
Answers
- c) both are acceptable – In a textbook context, either works, but formulae might feel more formal.
- a) formulas – An email to a team is a casual context; formulas is more natural.
- b) formulae – A doctoral thesis is formal academic writing; formulae is preferred.
- a) formulas – A spreadsheet context in a business setting calls for formulas.
Frequently Asked Questions
1. Is “formulae” still used in modern English?
Yes, but mainly in formal academic and scientific writing. In everyday English, formulas is far more common. You will rarely hear formulae in conversation.
2. Can I use “formulas” in a scientific paper?
It depends on the journal or style guide. Many modern scientific publications accept formulas, but some traditional ones still prefer formulae. Check the author guidelines or look at recent articles in the same journal.
3. What is the plural of “formula” in British English vs. American English?
Both British and American English use both forms. However, formulae is slightly more common in British academic writing, while formulas is more dominant in American English overall. The difference is small and not a strict rule.
4. Is it wrong to use “formulae” in an email?
It is not grammatically wrong, but it may sound overly formal or even pretentious in a casual email. For most business communication, formulas is the better choice.
For more help with tricky plural forms, visit our Confusing Plurals section. You can also check our Plural Spelling Rules for general guidance, or our Singular or Plural Checks for quick answers. If you have further questions, see our FAQ page or read our Editorial Policy to understand how we create these guides.
