CADR Rating Explained, How to Size an Air Purifier for Your Room
CADR tells you how much clean air a purifier puts out each minute. It is the number to start with when you size a unit for a room. Here is how it works and how to use it.
Last updated: October 2026 · By the CleanAirHomeLab team
What CADR Measures
CADR stands for Clean Air Delivery Rate. It is given in cubic feet per minute (CFM). The EPA says to choose a portable air cleaner with a CADR that is large enough for the room. The higher the CADR, the more particles the unit can filter and the larger the area it can serve.
Think of it like a faucet. CADR is how fast clean water comes out. A faucet that gives 5 gallons a minute fills a bathtub faster than one that gives 2. A higher CADR fills your room with clean air faster.
CADR is for particles only. The EPA says there is no widely used rating for how well a portable air cleaner removes gases.
CADR for Smoke, Dust and Pollen
Many makers publish three CADR numbers: one for smoke, one for dust and one for pollen. The three are often different on the same machine. Coway lists the AP-1512HH at 233 for smoke, 246 for dust and 240 for pollen. It lists the Airmega 400 at 328 for smoke, 328 for dust and 400 for pollen.
Some makers publish one number. Levoit lists a single CADR of 391 CFM for the Core 600S. When you compare two units, compare the same kind of number. AHAM's 2/3 rule uses the smoke CADR.
The 2/3 Rule
AHAM gives a rule of thumb: the CADR of your air cleaner should be at least two-thirds of the room's area. AHAM's example is a room that is 10 feet by 12 feet. That is 120 square feet, so it wants a smoke CADR of at least 80.
Quick Formula
Minimum CADR = room square footage x 2/3
Example: a 300 sq ft room x 2/3 = a CADR of about 200. The EPA chart lists 195.
This is for an 8-foot ceiling. With a higher ceiling, the EPA says you may want a higher CADR.
Why More CADR Has a Cost
More CADR usually means a bigger box and bigger filters. Coway's own figures show it. The AP-1512HH weighs 12.3 lb. The Airmega 400, with a higher CADR, weighs 24.7 lb.
So match the CADR to the room. Then check the maker's noise range, because a unit that is too loud ends up switched off.
Room Size Lookup Table
This is the EPA's sizing chart for particle removal. Find your room size and read off the minimum CADR.
| Room area | Minimum CADR (cfm) | Typical rooms |
|---|---|---|
| 100 sq ft | 65 | Small bedroom, home office |
| 200 sq ft | 130 | Bedroom, nursery |
| 300 sq ft | 195 | Large bedroom, small living room |
| 400 sq ft | 260 | Living room |
| 500 sq ft | 325 | Large living room |
| 600 sq ft | 390 | Open floor plan |
Room area and minimum CADR are from the EPA's Guide to Air Cleaners in the Home. The EPA notes the chart is for estimation and assumes an 8-foot ceiling. The "typical rooms" column is our own rough guide.
Know your room size? Go to the picks made for it: air purifiers for bedrooms, air purifiers for large rooms or whole-house air purifiers. Shopping by price? See purifiers under $100 and purifiers under $200.
Common CADR Myths
Myth: The room size on the box is the room size you get
Reality: Makers can quote room size at different air change rates. Coway rates the Airmega 400 at 3,120 sq ft at one air change an hour and 1,560 sq ft at two, from the same machine. It rates the AP-1512HH at 874 sq ft at two air changes an hour and 361 sq ft at 4.8. Check which rate the number is for.
Myth: CADR tells you how well a unit removes gases and odors
Reality: The EPA says the CADR rating system is for particles only. For gases, the EPA says activated carbon filters can work when a large amount of carbon is used.
Myth: The filter name on the box is all that matters
Reality: The filter tells you what gets caught. CADR tells you how much clean air comes out each minute. You need both to know if a unit fits your room.
Myth: Every good purifier has a CADR number
Reality: Not every maker publishes one. IQAir publishes no AHAM CADR for the HealthPro Plus, so you cannot compare it on CADR with units that do.
Common Questions
What does CADR stand for?
CADR stands for Clean Air Delivery Rate. It is given in cubic feet per minute (CFM). The EPA says a higher CADR means the unit can filter more particles and serve a larger area.
How do I work out the CADR I need for my room?
Use the 2/3 rule from AHAM: the CADR should be at least two-thirds of the room's floor area in square feet. AHAM's example is a 120 sq ft room, which wants a smoke CADR of at least 80. The EPA chart gives the same answer: 65 cfm for 100 sq ft, 195 cfm for 300 sq ft and 390 cfm for 600 sq ft.
What if my ceiling is higher than 8 feet?
The EPA chart assumes an 8-foot ceiling. The EPA says that if you have higher ceilings, you may want a portable air cleaner with a higher CADR.
Why do some purifiers have no CADR number?
Not every maker publishes one. IQAir publishes no AHAM CADR for the HealthPro Plus. That does not tell you the unit is good or bad. It means you cannot line it up against CADR-rated units.
Does CADR cover gases and odors?
No. The EPA says the CADR rating system is for particles only, and that there is no widely used rating for gas removal.
Know Your CADR. Pick Your Purifier.
Now you know what CADR means. Our picks list each maker's CADR, noise range and filter cost.
Affiliate Disclosure: Some links on this site earn commissions at no extra cost to you. Full disclosure.
Sources and last review
Specifications on this page are taken from the documents below, on the dates shown. We do not physically test products; read our methodology. Page last reviewed .
- US EPA (Guide to Air Cleaners in the Home) (government), retrieved 2026-10-04
- AHAM Verifide (Air Filtration Standards) (standards body), retrieved 2026-10-04
- Coway (manufacturer), retrieved 2026-09-03
- Coway (manufacturer), retrieved 2026-09-03
- Levoit (manufacturer), retrieved 2026-09-03
- IQAir (manufacturer), retrieved 2026-09-03