How To Choose An Air Purifier For All Room Size?

Knowing your room size is vital on your air purifier buying journey. Your air purifier is as good as useless when it cannot even cover the entire bedroom. In this post, we will discuss the jargons used to measure a room size and airflow performance. We will also talk about the different distance abbreviations from the manufacturers used to boost their figures. At the end of the guide, you will learn how to measure and calculate the exact square footage needed to cover a room.
Short answer
CADR x 1.55 = Room size in square feet.
ft2 x ft (ceiling height) = Room size in cubic feet.


How Big of An Air Purifier Do I Need?

First, you will need to calculate the room size needed for air purification. Measure the length and width of the room, then multiply the numbers to get the room square footage. If you want to size an air purifier for multiple rooms, get each room size figures and add up the total. For example, you have a living room that is 200 square feet and a dining area that is 180 square feet, the total square footage to purify the two rooms will be 200 + 180 = 380. You will need an air purifier with a CADR to handle 380 square feet of coverage. To calculate the air purifier capacity in cubic feet, multiply the square footage of the room by the ceiling height.

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. CADR indicates the volume of filtered air from an air purifier in cubic feet per minute (CFM). The higher the 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 in the manual. You can also find out more information about the CADR ratings on AHAM 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?

Following AHAM’s 2/3 rule, the air purifier CADR must have a minimum two-thirds of a room-size in square feet. To cover a 200 square feet room, the CADR must be at least 133 cfm. Obviously the higher the CADR output, the faster and more air it can cover.

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

Not all air purifiers are created equal. Some models are only meant for minuscule room size while others can even cover the entire living hall. The below table is a quick calculation guide on CADR needed to purify 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

Again coming from AHAM guideline, multiple 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, is that simple. This is the official AHAM formula 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

So is that simple? Not quite, as the above calculation is based on an ideal situation with consistent output at one air exchange per hour. According to Oransi, you need to take the ceiling height into account as well. A better measurement would be in cubic feet. Instead of just calculating the length and width of a room, we need to take in the height of the ceiling value. For example, a 200 square feet room size with a 10 feet high ceilings means the room is at 2000 cubic feet.

Our take? Ignore the ceiling height as it makes the whole calculation more difficult to measure. Since CADR is only meant to be a guideline determining what air purifier size is needed, just 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 test lab in New York. 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 existence is to create a standardized measurement that can be used by all brands. This protects the consumers from being misled by the manufacturers in performance figures. The problem is CADR relies on airflow distribution and some air purifiers do not focus on that. A good example would be Airfree’s Thermodynamic TSS Technology that uses heat rather than airflow. Another issue is CADR tests are conducted in the highest fan speed setting not the overall speed. A big disadvantage to manufacturers that offers multiple speed for better usability. CADR test also does not measure the air filter performance over time.

The quality of the filter will have a direct impact on the figures which are not accounted by CADR. For example, a True HEPA filter has a denser setup thus creates 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 but the CADR score favors the thin carbon sheet more. Add-on filtration like UV-light and ionizer are also left out in the CADR test and so are gas particles smaller than 0.3 microns. With all that, now you understand why some manufacturers are not willing to participate in the AHAM certification program.

What About Air Purifier Room Size? Is it Dependable?

It is but you are relying on the manufacturers themselves to provide you with the input. They might boost their numbers in a controlled environment such as an empty room or short ceiling height. A few bad eggs manufacturers might even mislead the user with cubic feet numbers than square feet. The area of the room is not the same as the Surface area of the room. Another common tactic is the use of lower air changes per hour to display bigger numbers. Air changes our hour (ACH) refers to how many times an air purifier can filter the entire volume of air in a designated room every hour. For example, a 200 sq. ft. coverage at 2 air changes per hour is cut down to half (100 sq. ft.) at 4 air changes per hour. Most brands will display the 200 square footage coverage with a small disclaimer note.

How Big Of An Air Purifier Do I Need?

Choosing the right size air purifier is very important to remove dust, allergens, germs, smoke, and odors in a room. After you have determined the room size square footage needed for air purification, measure the space on where you intend to place the air purifier. To get the most out of your air purifier, we will calculate the room size requirement based on 2 air changes per hour:

  • 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.
  • Medium room size (lounge, studio, small basement, bathroom with attached bathtub) – Go with a mid-range air purifier that can cover between 201 to 399 square feet.
  • 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 – Can be customized according to your house floorplan. Costly the troublesome to setup.

A person with hypersensitivity or asthma will need a HEPA air purifier with double airflow output to help manage their symptoms. In other words, the air purifier needs to clean the air at 4 changes per hour to thoroughly remove microscopic allergens in the air. The higher cleaning frequency protects an asthmatic person from breathing into the harmful particles. As such, the official air purifier’s recommended room size will need to be cut down to half from the above guideline.

If CADR And Room Size is Not The Answer, What Can I Depend On?

Yourself. By that I mean do your own research and comparison and determine what is best for your needs. CADR or the air purifier room size is a good place to start. Then branch out to the filters depth, technology used, and cleaning mode. While you’re at it, consider the dimension, power consumption, and noise level. Finally, look out for the brand reputation and maintenance as it will impact the air cleaner longevity.

The perfect place to start is in our compare air purifiers page. You can then check out other user reviews on Amazon before putting down your money.

According to Market Watch, the Air Purification Systems Market is forecast to exceed more than US$ 24 Billion by 2024. An increase 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. This 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. Our job is to give you a better insight into the air cleaner and see how much square footage it can cover in a room.

Frequently Asked Questions FAQ

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 it can cover more space and multiple rooms with open doors. A small air purifier is only sufficient to clean the air in a single room. However, 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. If you need to cover a single room with a known dimension, measure the room size then opt for the right size air purifier.

Will a Small Air Purifier Work In a Large Room?

A tabletop, small air purifier is not effective in a large room due to its limited air filtering capacity and compact size. A large air purifier can cover multiple rooms at the same time with all doors open. Instead of going for a large air purifier straight, measure the room size to get the perfect model without the extra cost and bulkiness. The right size air purifier can remove airborne dust, mold, pollen, pet dander, germs, and smoke in the room.

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.