'Indoor' or 'Indoors'? What Is the Difference? | Mastering Grammar

(Last Updated: 1 April 2025)

Indoor vs Indoors: Understanding the Difference

Indoor is an adjective that is only used before a noun. It describes something located, done, or used inside a building:

✅ How much does it cost to build an indoor swimming pool?

✅ The indoor track at the gym is perfect for running in any weather.

✅ I prefer indoor workouts.

✅ During the winter, we enjoy indoor activities like board games and movie nights.

✅ These shoes are meant for indoor wear only.

Indoors, in contrast, is an adverb. If you go indoors, you enter a building. Similarly, if you do something indoors, you do it inside a building:

✅ As it was rainy, we decided to stay indoors.

✅ Please remember to take off your shoes before coming indoors.

✅ During the winter, we prefer to exercise indoors at the gym.

✅ I enjoy reading books indoors on a rainy day.

✅ This year, the fun fair will be held indoors, unlike previous years.

The entry for the adverb indoors in the Oxford Advanced Learner's Dictionary

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Examples from the Media

Ontario customers at the gym and restaurant, and guests at a wedding have to be vaccinated, but there is no government mandate for employees. So indoor settings such as dining, where masks are removed, are not going to be safe enough for some of us. —Toronto Star (2021)

Don't we want cleaner indoor air at all times? Why not apply higher standards to every new building and every new renovation? —The Washington Post (2023)

New York residents are being warned to 'just stay indoors' as scorching temperatures bake the Big Apple, while much of the country sweats out one of the hottest heatwaves in years. —Daily Mail (2023)

A presumed lioness is on the loose in Berlin, where residents in some areas were warned to stay indoors as scores of police tried to track the animal down. —The Sydney Morning Herald (2023)

Practice

Choose the correct word to complete each sentence.

1. The cat prefers to stay indoor/indoors and nap on the comfortable couch.

2. The storm was raging outside, but we felt safe and warm indoor/indoors.

3. The indoor/indoors climbing gym offers a variety of challenging routes for climbers.

4. We set up an indoor/indoors garden with lots of potted plants.

5. We had a cosy evening indoor/indoors, curled up by the fireplace.

6. The indoor/indoors playground is a popular attraction for children on rainy days.

7. Julia prefers to do her workouts indoor/indoors to avoid the heat and humidity.

8. We had an exciting game of indoor/indoors basketball during our team practice.

Answer Key

1. indoors    2. indoors    3. indoor    4. indoor    5. indoors    6. indoor    7. indoors    8. indoor

Recommended Further Reading

'Outdoor' or 'Outdoors'? What Is the Difference?

Real-World Examples of Misuse

Indoor is an adjective and indoors is an adverb. In this sentence, the adverb form should be used to modify the verb phrase wear a jacket, indicating where a jacket is worn.
(Image Source: 香港中學文憑試: 英文星級句子全攻略)

1. The correct spelling of the word is government.
2. The definite article the is not needed when referring to a general group of people in this context.
3. Travel up to the mountain implies merely reaching the base of the mountain rather than ascending it. By removing the preposition to, the sentence becomes more focused on the action of moving upwards, which is likely the intended meaning in the context of the government warning.
4. The adverb indoors should be used to modify the verb stay. Indoor is an adjective and would be used differently, such as in indoor areas.
5. The verb states would be more appropriate for the context of a weather forecast, which typically presents information in a declarative and definitive manner. Mentioned implies a casual reference, which might not convey the intended certainty of a weather forecast. Using states strengthens the assurance that no precipitation is expected, thereby supporting the recommendation not to bring an umbrella.
6. The phrase these runs might imply that they are still considered runs despite being off the designated paths. Changing it to these areas clarifies that the skiers are moving into undesignated or unmarked areas.
7. Using the modal verb may emphasises that the movement of skiers may cause the snow to loosen, rather than implying that it always does.
(Source: St. Paul's Convent School, Primary Section)
(Also by the Same School: 1/2/3/4/5/6/7/8/9/10/11)