A good CADR rating depends on your room size, but as a general benchmark, most people shopping for a living room or bedroom air purifier should look for a smoke CADR of at least 130 to 260 cfm. The EPA provides a simple formula: your air purifier’s CADR should be roughly two-thirds of the room’s square footage, assuming standard 8-foot ceilings. So for a 300-square-foot room, you’d want a minimum CADR of about 195 cfm.
What CADR Actually Measures
CADR stands for Clean Air Delivery Rate, and it tells you the volume of filtered air an air purifier delivers per minute, measured in cubic feet per minute (cfm). It’s not just about how good the filter is. CADR combines two factors: how efficiently the filter captures particles and how much air the fan pushes through it. A purifier with a perfect filter but a weak fan will have a lower CADR than one with a slightly less efficient filter and a powerful fan.
This distinction matters because you’ll often see brands advertising “HEPA filtration” that captures 99.97% of particles, which sounds impressive on its own. But a HEPA filter with a low airflow rate will clean a room slowly. A purifier rated at 50 CADR could mean it pushes 100 cfm of air through a filter that catches 50% of particles, or it could mean it pushes 50 cfm through a filter that catches everything. The end result for your room air is the same either way.
The Three Pollutant Categories
CADR isn’t a single number. Air purifiers are tested against three types of particles, each a different size:
- Smoke: The smallest particles tested, ranging from 0.09 to 1.0 microns. This is the most demanding test and typically produces the lowest CADR number.
- Dust: Mid-range particles between 0.5 and 3 microns, including dust mite debris.
- Pollen: The largest particles at 5 to 11 microns. Most purifiers score highest here because bigger particles are easier to capture.
When comparing models, pay the most attention to the smoke CADR. It’s the hardest test to score well on, and if a purifier handles fine smoke particles effectively, it will handle dust and pollen even better. The smoke number is also the one used in most sizing recommendations.
Minimum CADR for Common Room Sizes
The EPA publishes a sizing chart based on 8-foot ceilings. Here’s what you need at minimum:
- 100 sq ft (small bedroom): 65 cfm
- 200 sq ft (standard bedroom): 130 cfm
- 300 sq ft (large living room): 195 cfm
- 400 sq ft (open-plan space): 260 cfm
- 500 sq ft (large open area): 325 cfm
- 600 sq ft: 390 cfm
If your ceilings are higher than 8 feet, bump up to the next tier. A 300-square-foot room with 10-foot ceilings holds 25% more air, so you’d want a CADR closer to 245 cfm rather than 195.
For wildfire smoke specifically, the Association of Home Appliance Manufacturers (AHAM) recommends a stricter standard: your smoke CADR should equal the full square footage of your room, not just two-thirds. So that same 300-square-foot room would need a smoke CADR of 300 during fire season.
How CADR Relates to Air Changes Per Hour
Another way to think about CADR is how many times per hour a purifier can cycle all the air in your room through its filter. Health-focused settings like dental offices target 15 air changes per hour, but for a typical home, 4 to 6 air changes per hour is a reasonable goal. A higher CADR in a smaller room means more air changes per hour and faster cleaning after cooking, vacuuming, or opening windows.
If you already know your room’s volume (length × width × ceiling height in feet), you can estimate air changes per hour by multiplying the CADR by 60 (to convert from per-minute to per-hour) and dividing by the room volume. A purifier with a CADR of 200 in a 300-square-foot room with 8-foot ceilings would deliver about 5 air changes per hour, which is solid for residential use.
The Noise Tradeoff
CADR ratings are measured at the purifier’s highest fan speed, which is also its loudest setting. In practice, most people don’t run their purifier on max all the time. On low or sleep mode, air purifiers typically produce 22 to 30 decibels, quieter than a whisper. Medium settings land around 40 to 50 decibels, noticeable but manageable. High settings can reach 60 to 65 decibels, roughly the volume of a normal conversation.
This means the CADR you see on the box represents peak performance, not what you’ll get during everyday use at a comfortable noise level. Buying a purifier with a higher CADR than your room technically requires gives you headroom. You can run it on a medium or low setting, keep the noise down, and still get adequate filtration. If you buy one that just barely meets the minimum, you’ll need to run it on high constantly to get the rated performance.
What CADR Doesn’t Cover
CADR only measures how well a purifier removes particles from the air. It tells you nothing about gases, odors, or chemical vapors like volatile organic compounds (VOCs). These include fumes from paint, cleaning products, new furniture, and cooking. Removing gaseous pollutants requires different technology, typically activated carbon filters, and there’s no standardized rating equivalent to CADR for gas removal. If chemical sensitivity or odors are your main concern, look for purifiers with substantial activated carbon filters in addition to a good CADR rating, and know that the carbon filter’s effectiveness varies with temperature and humidity.
Picking the Right Number
Start by measuring your room. Multiply length by width to get the square footage, then multiply that by two-thirds to find your minimum smoke CADR. If you live in an area affected by wildfire smoke, use the full square footage instead. Then add a buffer. Buying 20 to 30% above the minimum lets you run the purifier at a quieter setting while still filtering effectively.
For a typical 250-square-foot bedroom, that means a smoke CADR of at least 165, ideally closer to 200. For a 400-square-foot living room, aim for at least 260, ideally 300 or above. Look for models tested and verified by AHAM, which runs an independent certification program. Not all manufacturers participate, but those that do have their CADR claims independently verified rather than self-reported.