How To Choose An Air Purifier For All Room Size?

Knowing your room size is vital to your air purifier buying journey. Your air purifier is as good as useless when it cannot cover the entire bedroom. In this post, we will discuss the jargon used to measure room size, CADR, and airflow performance. We will also explore the different distance abbreviations from each manufacturer and what they do to boost their figures. At the end of the guide, you will learn how to calculate and determine what size air purifier you need.


According to Market Watch, the Air Purification Systems Market is forecast to exceed more than US$ 24 Billion by 2024. An increase of 8% projections of the compound annual growth rates (CAGRs) from 2015. As the global market trends continue to surge, big brands are pumping out more and more models. It creates confusion for the consumer market with the expanded selection of HEPA air purifiers available. Many consumers would go for the cheaper but wrong type of air purifier that fails to clean the entire room. To avoid the same mistake, we will teach you how to find the right size air purifier based on the suggested room size and CADR.

How Big of An Air Purifier Do I Need?

Before purchasing an air purifier, it’s vital to know where you intend to use it. Whether for a single bedroom, living room, basement, kitchen, or multiple rooms, you need to account for the total room sizes. With that information, you will know how “big” an air purifier you are looking for. For example, A 300 square footage room requires an air purifier with a suggested room size of a minimum of 300 sq. ft. at 2 air changes per hour. Alternatively, you can get 2 smaller air purifiers with the combined airflow capacity to cover at least 300 square footage of room sizes.

Room size matter for an air purifier. If you are unsure about your room size, you will need to calculate the room area on where you intend to place the air purifier. Measure the length and width of the room, then multiply the numbers to get the room’s square footage. E.g. 10 (length) x 11 (width) = 110 square feet. If you want to use a large air purifier for multiple rooms, get each room size measurement and add up the total. For example, combine a 200 square feet living room with a 180 square feet dining area, and the total square footage to purify the two rooms will be 200 + 180 = 380.

In short, choosing the right size air purifier is very important as it affects how well it can remove dust, allergens, germs, smoke, and odors in a room. To help you get started, below are the four categories you will typically find in a residential air purifier.

  • Small room size (bathroom, bedroom, personal working space) – Go with a small air purifier e.g. desktop or mini tower design, that can cover up to 200 square feet of room size.
  • Medium room size (lounge, studio, small basement, dry bathroom) – Go with a mid-range air purifier that can cover between 201 to 399 square feet of room size.
  • Larger room size (living hall, master bedroom, office, basement, garage) – Go with the top-of-the-line air purifier that can cover 400 square feet and above.
  •  Whole-house air purifier – Customizable according to your house floor plan. Costly and troublesome to set up.

A quick note: People with hypersensitivity or asthma will need a HEPA air purifier that cycles clean air at 4 changes per hour or every 15 minutes. The higher air cleaning frequency protects an asthmatic person from breathing into harmful particles. As such, the manufacturer’s air purifier’s suggested room size will need to be cut down to half for those that fall into the special group.

Manufacturer's suggested room size

What Is CADR?

Clean Air Delivery Rate (CADR) is a standard measurement developed by AHAM to allow consumers to compare air purifiers’ performance. It is recognized by the U.S. Environmental Protection Agency (EPA) and American Lung Association. Tested on three different pollutants (dust, pollen, smoke), CADR indicate the volume of filtered air released from an air purifier hourly in cubic feet per minute (CFM). The higher the CADR numbers, the faster and more clean air the unit can deliver.

CADR test is conducted by The Association of Home Appliance Manufacturers under the program AHAM Verifide. The test will be performed independently on noise level and air filtration performance: dust, pollen, and smoke. Each test will determine the air purifier’s effectiveness in removing the specific pollutant types. The result is usually printed on the air cleaner’s box or manual. You can also find out more information about the CADR ratings on AHAM’s official website.

Now you have a basic understanding of CADR, Let’s move on to the main topic.

AHAM certificate

What Is The CADR Needed To Cover a Room?

To find out what size air purifier you need, use AHAM’s 2/3 rule. The CADR of the air purifier must be at least two-thirds of the room size. For example, to cover a 200 square feet room, the CADR must be at least 133 cfm. Again, the higher the CADR output, the faster and more clean air can be distributed. Now you have a basic understanding of CADR, Let’s move on to the main topic.

Room size (sq. ft.) x 2 / 3 = Air Purifier’s minimum CADR

With that, you can tell that not all air purifiers are created equal. Some models are only meant for minuscule room sizes, while others can even cover the entire living hall. The below table is a quick calculation guide on CADR needed to purify the air of a specific room size.

Room dimensions (ft)Ceiling height (ft)Total volume (ft3)CADR needed in ft3/h
10 x 10880065
11 x 11896878
12 x 1281,15293
13 x 1381,352109
14 x 1481,568126
15 x 1581,800145
16 x 1682,048165
17 x 1782,312186
18 x 1882,592209

How To Measure a Room Size based on CADR

Following the AHAM guideline, multiply the CADR value by 1.55. For example, an air purifier with a smoke CADR of 300 cfm can cover up to 465 square feet of room size. Yup, it is that simple. The official AHAM formula is based on the CADR requirement to remove 80% of particles, at the assumption of one room air exchange per hour.

CADR (cfm) x 1.55 = Room size in square feet

The above calculation is based on an ideal situation with consistent output at one air exchange per hour. A more precise measurement would be in cubic feet, where you also need to take the ceiling height into account. To calculate the air purifier capacity in cubic feet per minute, multiply the room’s square footage by the ceiling height.

Room size (sq. ft.) x Ceiling height (ft) = Volume of indoor air (ft³)

For example, a 200 square feet room size with 10 feet high ceilings equals 2000 cubic feet. Vice versa, to get the cubic feet per minute, use the following calculation:

Volume of indoor air (ft³) x Air Changes per Hour / 60 min = Cubic feet per minute (cfm)

Our take? Ignore the ceiling height, as it makes the calculation more difficult to measure. Since CADR is only meant to be a guideline to determine what air purifier size is needed, stick with the square footage numbers.

 Air Changes Per Hour (ACH)Recommendation
100155785239PureZone 3-in-1
1502331177838Levoit LV-H132
20031015510350Winix 5500-2
300465232155116Honeywell HPA300
350543272181136Airmega 400S

Can We Rely on The CADR Numbers?

CADR numbers are reliable and a good metric as it is tested independently in a certified New York test lab. However, CADR is not without its flaw, and there are more factors to account for. Let’s address the common issue one by one.

CADR’s existence is to create a standardized measurement that all brands can use. It protects the consumers from being misled by the manufacturers in coming out with their own performance figures. The problem is that CADR relies on airflow distribution volume, and not all air purifiers focus on that. A good example would be Airfree’s Thermodynamic TSS Technology, which uses heat to clean the air rather than the volume of clean air. Another issue is CADR tests are conducted in the highest fan speed setting, not the overall speed. CADR test also does not measure the air filter performance over time.

The quality of the filter will also have a direct impact on CADR output. For example, a True HEPA filter has a denser setup, thus creating a stronger airflow resistance than an inferior HEPA-type filter. A 15 lbs Activated Carbon filter is a better smoke filtration than a carbon sheet. Still, the CADR score favors the thin carbon sheet more. Add-on filtration, like UV light and ionizer, is left out of the CADR test. Fine particles smaller than 0.3 microns are also excluded. With all that, now you understand why some manufacturers are unwilling to participate in the AHAM certification program.

What About Manufacturer’s Suggested Air Purifier Room Size? Is it Dependable?

It is, but you are relying on the manufacturers to provide you with the input. They might boost their numbers in a controlled environment, such as an empty room or a shorter ceiling height. A few bad egg manufacturers might even mislead the user with cubic feet than square feet. Another common tactic is using lower air changes per hour to display more significant numbers. Air changes our hour (ACH) refers to how often an air purifier can filter the entire air volume hourly in a designated room. You’re getting a 200 sq. ft. coverage at 2 air changes per hour and only 100 sq. ft. at 4 air changes per hour.

what size air purifier do I need

Can An Air Purifier Be Too Big For a Room?

It's always better to go with a bigger air purifier than a smaller one as the stronger airflow can cover more air cleaning space and even multiple rooms with open doors. A small air purifier with limited airflow is only sufficient to clean the air in a single room. As for drawbacks, a large air purifier can be big and bulky; thus, it will take up a lot of room space. Running cost is also much higher due to the extra airflow output, higher energy consumption, and larger filters. If you need to cover a single room with a known dimension, measure the room size and opt for the right size air purifier.

Will a Small Air Purifier Work In a Large Room?

A tabletop/ small air purifier works but is ineffective in a large room due to its limited air filtering capacity and compact size. Instead, go with a large air purifier that has the airflow performance to remove airborne dust, mold, pollen, pet dander, germs, and smoke in a large room. Again, measure the room size and choose the right size air cleaner to avoid paying the extra cost and bulkiness.

Do Air Purifiers Work With High Ceilings?

Air purifiers do work in a room with high ceilings above 8 feet. Due to the larger air cleaning space, it is advisable to go with a large air purifier that exceeds the 400 sq. ft. suggested room size requirements, such as Coway Airmega, IQAir HealthPro Plus, or Alen BreatheSmart.

Does An Air Purifier Clean The Whole House?

A built-in whole-house air purification system is designed to clean the air as it passes through your home's HVAC system. However, even if you opt for a whole-house air purifier setup, it will only partially clean the house as many household items would impede the airflow circulation. A better option would be having multiple air purifiers in every room that you can use to target airborne contaminants effectively.

Final Thoughts

CADR and room size are not the ultimate answer. While the numbers will give you a better insight into the air cleaner, you will still need to research and determine what is best for your needs. So branch out your research to the depth of the filters, the technology used, the cleaning mode, and the reliability of the particular model. Consider other usability factors such as dimension, power consumption, and noise level. Lastly, the brand reputation, cost, and maintenance will also impact the air cleaner longevity. The perfect place to start is our compare air purifiers page and see what's available.

Max Fernandez

A loving father and a dedicated reviewer for airfuji.com with more than 1000 air purifiers under his belt. Max Fernandez is also one of the million patients currently suffering from asthma. Feel free to nudge him if you have any questions.
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