Here is the dirty secret of air purifier shopping: the number that matters most is the one most boxes hide in the fine print. It is called CADR, and it decides whether a purifier cleans your room or just sits there glowing.
CADR stands for Clean Air Delivery Rate. It measures how many cubic feet of clean air a purifier delivers each minute, tested for smoke, dust and pollen under the AHAM AC-1 standard. Bigger number, faster cleaning. Below, find how to match the number to your room, plus real picks at each level with current Amazon prices.
Table of Contents
What CADR is, and why it beats brand names
AHAM, the trade group that runs the test, gives a simple rule: the smoke CADR should be at least two-thirds of the room’s square footage. A 300 sq ft room needs a smoke CADR of about 200. Not 300. Not 100. About 200.
A CADR 500 unit cleans the air twice as fast as a CADR 250 unit. For allergies and asthma, speed matters, because allergens spend less time floating around your nose. For the full test explained, read our guide to how to read a CADR rating.
Here is where shoppers get burned. A $1,000 purifier with a low CADR can lose to a $230 one with a high CADR in the same room. Price tells you about the brand, the finish and the app. CADR tells you about the cleaning.
- CADR is the real measure of air cleaning speed.
- Higher CADR means more air changes per hour.
- Match the number to the room, not to the box art.
- Check that the CADR comes from AHAM, not from a marketing page.
CADR by room size
| Room size | Target smoke CADR | Typical rooms |
|---|---|---|
| 100-200 sq ft | 70-135 | Bedrooms, home offices, nurseries |
| 200-400 sq ft | 135-270 | Master bedrooms, living rooms |
| 400+ sq ft | 270+ | Open-plan spaces; use two units if needed |
Ceiling height matters too. The AHAM rule assumes standard 8-foot ceilings. Vaulted ceiling? Move up one size.
One more trick: if wildfire smoke or heavy pollen is a regular visitor, aim higher than the minimum. A purifier that completes five air changes an hour handles a bad day better than one that barely keeps up on a good day.
How to check a CADR claim
Not every CADR on a box is real. The only way to know is to look for the AHAM Verifide seal and search the unit in the AHAM directory. Watch for these red flags:
- A single “CFM” number with no split between smoke, dust and pollen.
- Phrases like “up to” or “equivalent to” next to the number.
- A CADR that is far higher than similar units with the same fan size.
- No model number in the AHAM directory.
Expect more of this as listings multiply: unverified CADR numbers will keep spreading on marketplaces, so the check above gets more useful, not less. One honest exception: IQAir does not use the AHAM test, so its coverage claims come from the maker. That is fine for a premium brand with a long record, but it means no apples-to-apples comparison.
The math behind air changes per hour
Air changes per hour (ACH) tells you how often the whole room’s air goes through the filter. The formula is CADR times 60, divided by the room volume in cubic feet. Here is how that works out for the picks below in a typical room with 8-foot ceilings.
| Purifier | Smoke CADR | ACH in 200 sq ft | ACH in 300 sq ft | ACH in 400 sq ft |
|---|---|---|---|---|
| Levoit Core 300 | 143 | 5.4 | 3.6 | 2.7 |
| Coway AP-1512HH Mighty | 233 | 8.7 | 5.8 | 4.4 |
| Winix C545 | 232 | 8.7 | 5.8 | 4.4 |
A common target for allergy and smoke control is four or more air changes an hour. That is why the Levoit works in a bedroom and gets stretched in a 400 sq ft room.
Best purifiers by CADR range
CADR 130 to 170: small rooms and bedrooms
The Levoit Core 300 is the standout here. Amazon lists a CADR of 143 for smoke, 153 for dust and 167 for pollen, good for about 222 sq ft at 4.8 air changes an hour. At $89.99 with a 4.7-star rating from more than 108,000 buyers, it is hard to beat for a bedroom. Levoit says to swap the filter about every six to eight months.
CADR 230 to 250: the sweet spot
The Coway Airmega AP-1512HH Mighty is rated at 233 for smoke, 246 for dust and 240 for pollen, which covers about 361 sq ft by the AHAM rule. It is a four-stage unit with a washable pre-filter, an auto mode that reads the air, and an eco mode that shuts the fan off when the air is clean. At $229.99 and 4.6 stars from nearly 29,000 buyers, it is the pick for living rooms and big bedrooms.
The Winix C545 lands in the same range: CADR 232 for smoke, 243 for dust and 246 for pollen, verified for 360 sq ft. It costs more, $273.42, but adds Wi-Fi and a two-year warranty. Our Winix C545 review covers the PlasmaWave switch in detail.
Big rooms and severe allergies
The IQAir HealthPro Plus XE is the premium pick. It runs about $1,199.99 and Amazon lists it for spaces up to 1,125 sq ft. One catch: IQAir does not submit the HealthPro Plus for AHAM CADR testing, so there is no official CADR to compare. Treat the coverage claim as the maker’s own number.
Quick comparison
Prices checked October 2026 and change often.
Mistakes that waste money
- Buying on watts or fan size instead of CADR.
- Putting the purifier behind a couch, where air cannot reach it.
- Running it only when the room feels dusty. Run it all day.
- Forgetting the filter. A clogged filter drops airflow, and CADR with it.
- Choosing a unit for the biggest room in the house, then using it in the smallest, or the reverse.
Fixing any one of those usually makes more difference than upgrading to the next price tier.
Where CADR is headed
Expect CADR to get a wider job. AHAM’s Verifide program already puts energy use next to CADR, and the industry has been working on test methods for gases and VOCs too. In a few years, a good box may list particle speed, gas removal and watts side by side.
That sounds like progress, and mostly it is. The risk is label overload. More tests mean more badges, and brands love a badge. Shoppers may end up comparing five numbers where one used to do the job, and cheaper brands will still print CADR claims that no lab ever checked. Until then, the AHAM directory is the lie detector.
The bottom line
Check the CADR first. Match it to the room using the two-thirds rule. Then pick on noise, filter cost and looks. Skipping that order is how people end up with a gorgeous purifier that does nothing in a living room.
For model-by-model help, see our best air purifiers for home guide and the price tier breakdown. Shopping for a bedroom? Start with the quietest bedroom models.
Frequently asked questions
What is a good CADR for a bedroom? For a 150 to 250 sq ft bedroom, a smoke CADR between 100 and 170 does the job. The Levoit Core 300 sits right in that range.
Does a higher CADR always mean a better purifier? For speed, yes. For noise and cost, not always. A unit that runs on high all night may be louder than a slightly bigger model that coasts on low.
Does the IQAir have a CADR? Not an official AHAM one. IQAir uses its own testing, so compare it by coverage and filter type, not by CADR.
How often should the filter change? Follow the maker’s schedule. Levoit says every six to eight months for the Core 300; heavy dust, pets or smoke shorten that.
Can two small purifiers beat one big one? Often, yes, in open or oddly shaped spaces. Two CADR 143 units give a combined 286, and they cover more corners.
Sources
- Association of Home Appliance Manufacturers (AHAM), AC-1 standard and Verifide directory
- U.S. Environmental Protection Agency, Guide to Air Cleaners in the Home
- Levoit, Coway, Winix and IQAir product pages
- Amazon product listings (prices and ratings, checked October 2026)
