Have you ever wondered whether to write vapour or vapor? Both spellings are correct, but the right choice depends on the type of English you are using. British English generally uses vapour, while American English uses vapor.
These words have the same meaning. They describe a substance in its gaseous form or a gas present in the air. You may see them in science books, weather reports, school assignments, and everyday conversations.
Although the difference is only one letter, spelling consistency matters. Using the correct version helps make your writing clear and suitable for your intended audience. In this guide, you will learn the difference between vapour and vapor, understand their meanings, explore practical examples, and discover which spelling to use in different situations.
What Is the Difference Between Vapour and Vapor?
The main difference between vapour and vapor is regional spelling. Both words refer to the same scientific concept and have the same pronunciation in most varieties of English.
British English, Australian English, and many other varieties commonly use vapour. American English uses vapor. Neither spelling is inherently more correct than the other.
For example, a British writer might describe water vapour rising from a hot cup of tea. An American writer would usually describe the same phenomenon as water vapor rising from the cup.
Here is a quick comparison:
| Feature | Vapour | Vapor |
| English variety | British English | American English |
| Meaning | A substance in gaseous form | A substance in gaseous form |
| Pronunciation | Same in most accents | Same in most accents |
| Example | Water vapour | Water vapor |
| Common usage | UK, Australia, and many other regions | United States |
| Scientific meaning | Same | Same |
The important point is that the meaning does not change when you remove the letter u. Your choice should depend on your audience, publication guidelines, or preferred English style.
What Does Vapour or Vapor Mean?
Vapour or vapor refers to the gaseous form of a substance that is normally liquid or solid under particular conditions. It can form when a substance evaporates, boils, or changes directly from a solid into a gas through sublimation.
Water vapor is a familiar example. When water evaporates from a puddle, some liquid water molecules enter the air as gas. This process can happen even when the water is not boiling.
In everyday language, people sometimes use the word vapor to describe visible mist or steam. However, pure water vapor is invisible. The white cloud you see above boiling water consists mainly of tiny liquid droplets formed as the warm, moist air cools.
Examples of Vapour and Vapor in Everyday Life
You can encounter vapor in many ordinary situations.
- Water vapor: Water in its gaseous state in the atmosphere.
- Steam: Water vapor is often used informally to describe the visible cloud above hot water, although the visible cloud contains tiny droplets.
- Fuel vapor: Gas released when gasoline evaporates.
- Chemical vapor: Gaseous material released by certain chemicals.
- Vapor pressure: The pressure exerted by a vapor in equilibrium with its liquid or solid form at a given temperature.
- Vaporization: The process through which a substance changes into a gas.
In British English, these terms are generally written as water vapour, fuel vapour, vapour pressure, and vapourisation or vaporisation, depending on the applicable spelling convention.
In American English, the usual forms are water vapor, fuel vapor, vapor pressure, and vaporization.
Vapour or Vapor: Which Spelling Is Correct?
Both spellings are correct. The correct choice depends on your audience and the style of English you follow.
Use vapour when writing for a British English audience. This spelling is also common in Australian English and other English varieties that follow British spelling conventions.
Use vapor when writing for an American English audience. It is the standard spelling used in most American publications, educational materials, and scientific communication.
Consider these examples:
British English:
- Water vapour collects in the atmosphere.
- The scientist measured the vapour pressure.
- Vapour rose from the heated liquid.
American English:
- Water vapor collects in the atmosphere.
- The scientist measured the vapor pressure.
- Vapor rose from the heated liquid.
All six sentences are grammatically correct. The only difference is the spelling convention.
If you are writing an article for a US audience, use vapor consistently. If your readers are primarily in the UK, use vapour. When writing for an international audience, follow the publication’s preferred style guide.
Why Does British English Use Vapour?
British English retains the spelling vapour, which reflects the historical development of the word in English. The term came through French from Latin roots associated with steam, exhalation, or vapor.
Over time, English spelling developed regional variations. Many British spellings retained the letter u in words ending in forms such as -our. Examples include colour, honour, favour, and vapour.
These spellings became established in British dictionaries, schools, books, and newspapers. As a result, vapour remains the conventional form in British English.
British spelling does not add u to every word that sounds similar. The spelling depends on the word’s history and accepted usage. For example, some words ending in -or remain unchanged in British English.
If you are following British English, it is best to write vapour alongside other British spellings where appropriate. Consistency makes your work look polished and professional.
Why Does American English Use Vapor?
American English generally uses vapor without the letter u. This spelling is part of a broader pattern in American English, where many words that traditionally end in -our in British English are written with -or.
Examples include:
| British English | American English |
| Vapour | Vapor |
| Colour | Color |
| Flavour | Flavor |
| Honour | Honor |
| Labour | Labor |
| Neighbour | Neighbor |
Spelling differences between American and British English developed over several centuries. American spelling was influenced by efforts to simplify and standardize written English, including the work of American lexicographer Noah Webster.
Today, vapor is the standard form in the United States. It appears in American dictionaries, scientific publications, school textbooks, and technical documents.
If your target readers are American, using vapor will generally make your content feel more familiar to them. It is particularly important to maintain the same spelling throughout an article rather than switching between American and British forms.
Vapour or Vapor in Different English-Speaking Countries
Although the United States generally uses vapor, spelling preferences differ across English-speaking regions.
| Country or region | Common spelling |
| United States | Vapor |
| United Kingdom | Vapour |
| Australia | Vapour |
| New Zealand | Vapour |
| Canada | Vapour is common; usage can vary by publication |
| International scientific writing | Follow the journal or organization’s style |
British spelling conventions are common in Australia and New Zealand. Canadian English uses a mixture of British and American conventions, so the preferred form may depend on the publisher or institution.
Scientific and technical organizations may have their own editorial standards. Some use American English throughout their publications, while others follow British or international conventions.
When writing for a particular country, do not assume every word follows the same regional rule. Check a trusted dictionary or the style guide used by your school, company, or publication.
Vapour vs. Vapor: Meaning and Examples
Understanding the spelling difference is easy once you see both forms in context. The words mean the same thing, so the sentence does not change its basic meaning when you switch between them.
Examples Using Vapour
Here are some sentences using the British spelling:
- Water vapour plays an important role in Earth’s weather.
- The cold window became wet as moisture condensed from the air.
- The scientist studied the movement of vapour inside the chamber.
- Fuel vapour can escape from an improperly sealed container.
- The liquid produced vapour when the temperature increased.
- The weather report discussed the amount of water vapour in the atmosphere.
Examples Using Vapor
These sentences use the American spelling:
- Water vapor plays an important role in Earth’s weather.
- The cold window became wet as moisture condensed from the air.
- The scientist studied the movement of vapor inside the chamber.
- Fuel vapor can escape from an improperly sealed container.
- The liquid produced vapor when the temperature increased.
- The weather report discussed the amount of water vapor in the atmosphere.
Notice that each pair expresses the same idea. Only the spelling changes.
Water Vapour or Water Vapor?
The phrase water vapour is standard in British English, while water vapor is standard in American English. Both describe water in its gaseous state.
Water vapor is an important part of the water cycle. It enters the atmosphere through evaporation and transpiration. When moist air cools sufficiently, water vapor can condense into liquid droplets or ice crystals, contributing to clouds and precipitation.
The phrase is also common in discussions of humidity, climate, meteorology, and atmospheric science. When writing about these subjects, choose the regional spelling that matches your audience.
Common Words Related to Vapour and Vapor
The spelling difference appears in several related words. If you choose British English, remember that related terms may also use British spelling patterns.
| British English | American English | Meaning |
| Vapour | Vapor | Gaseous form of a substance |
| Vapour pressure | Vapor pressure | Pressure exerted by a vapor |
| Vapour trail | Vapor trail | Visible trail formed by condensation or ice crystals behind an aircraft |
| Vapour cloud | Vapor cloud | A cloud of gaseous material |
| Vapourise | Vaporize | To convert a substance into vapor |
| Vapourisation | Vaporization | The process of converting a substance into vapor |
| Vapouriser | Vaporizer | A device that produces vapor |
Some related spellings can vary depending on the dictionary and regional convention. In British English, vaporise and vaporisation are also encountered, particularly in scientific contexts. Follow your chosen dictionary or style guide instead of assuming that every related term must use the same pattern.
In the United States, vaporize and vaporization are the usual forms. These terms appear in chemistry, physics, engineering, and everyday explanations of phase changes.
How to Remember the Correct Spelling
A simple way to remember the difference is to associate vapour with British English and vapor with American English.
You can also use the spelling of familiar words as a reminder. British English often uses colour, favour, and honour. American English generally uses color, favor, and honor. The same regional pattern applies to vapour and vapor.
Try these quick tips:
- Writing for the UK? Use vapour.
- Writing for the US? Use vapor.
- Writing for Australia or New Zealand? Vapour is generally preferred.
- Writing a scientific paper? Follow the journal’s style guide.
- Editing an existing document? Keep the spelling consistent with the rest of the text.
You can also set your word processor’s language preference to British English or American English. This helps identify inconsistent spellings while you write.
For online articles, consider your intended audience before drafting. If most of your readers are in the United States, use American spelling throughout the article, including headings, tables, examples, and frequently asked questions.
Common Mistakes When Using Vapour or Vapor
Although the difference is straightforward, writers sometimes make mistakes when choosing between these words.
1. Mixing British and American Spelling
One common mistake is using vapour in one paragraph and vapor in another without a clear reason.
This does not usually make the writing grammatically incorrect, but it can make the article appear inconsistent. Choose one spelling convention and apply it throughout the document.
2. Assuming One Spelling Is Incorrect
Neither spelling is wrong. Both are accepted forms of the same word.
The mistake occurs when a writer treats one regional spelling as universally correct. Remember that language standards differ across countries.
3. Confusing Vapor With Smoke
Vapor and smoke are not the same thing. Vapor refers to the gaseous form of a substance, while smoke contains airborne particles and gases produced by combustion or related processes.
A visible cloud above a hot drink is usually made up of tiny liquid droplets, not visible pure water vapor.
4. Using the Wrong Related Word
If you use vapour in British English, check related terms such as vapourisation and vapour pressure against your preferred dictionary. If you use American English, vaporization and vapor pressure are the usual forms.
5. Ignoring the Intended Audience
A spelling choice should reflect the people who will read your content. A US school assignment, a British newspaper article, and an Australian website may follow different spelling conventions.
Choosing the appropriate form improves consistency and helps readers recognize that your writing follows a clear editorial standard.
Vapour or Vapor in Science and Everyday Writing
The words vapour and vapor are widely used in science, education, engineering, weather reporting, and ordinary conversation.
In chemistry, the term describes the gaseous phase of a substance under specified conditions. In meteorology, water vapor is an important component of the atmosphere and affects humidity, cloud formation, and the water cycle.
In engineering, vapor pressure can help explain how liquids behave under different temperatures and pressures. In everyday writing, the word may describe moisture in the air or gaseous material released from a liquid.
The spelling does not alter the underlying scientific concept. A British scientific paper may use vapour pressure, while an American paper may use vapor pressure. Both terms refer to the same physical property.
When preparing a technical report, prioritize accuracy as well as spelling. Use the scientific term that best describes the process, and avoid treating visible steam, smoke, mist, and vapor as interchangeable concepts.
For educational content, it is helpful to define the word on its first use. For example: “Water vapor, the gaseous form of water, is present in the atmosphere.” After that, use the term consistently.
Frequently Asked Questions
1. Is it vapour or vapor?
Both spellings are correct. Vapour is the standard British English spelling, while vapor is the standard American English spelling.
2. Which spelling is correct in American English?
Vapor is the correct standard spelling in American English. It is used in phrases such as water vapor, vapor pressure, and vaporization.
3. Is vapour British or American English?
Vapour is primarily the British English spelling. It is also commonly used in Australia, New Zealand, and other regions that follow British spelling conventions.
4. Do vapour and vapor mean the same thing?
Yes. Both words refer to the gaseous form of a substance, particularly one that is normally liquid or solid under particular conditions. The difference is regional spelling, not meaning.
5. How do you spell water vapor in the UK?
In the UK, the standard spelling is water vapour. In the United States, the phrase is generally written as water vapor.
6. Why does British English add a U to vapour?
British English retains the traditional -our spelling in words such as vapour, colour, and honour. American English generally uses the shorter -or forms.
7. Should I use vapour or vapor in formal writing?
Use the spelling preferred by your audience or publication. Choose vapour for British English and vapor for American English, and keep the choice consistent throughout your document.
Final Thoughts
The difference between vapour and vapor is simple: both words are correct, but they belong to different spelling conventions. British English generally uses vapour, while American English uses vapor. Both forms have the same meaning and pronunciation in most English accents.
If you are writing for a US audience, choose vapor. If you are writing for readers in the UK, Australia, or New Zealand, vapour is generally the better choice. When a publisher or organization provides a style guide, follow its instructions.
Ultimately, good writing is about clarity, accuracy, and consistency. Once you know your audience, choosing between vapour and vapor becomes an easy decision.
