What Size Air Purifier Do I Need (2026): CADR by Room Size

The size of air purifier you need depends on your room's floor area and ceiling height, and on the purifier's CADR (clean air delivery rate), not on the large "covers 1,700 sq ft" number printed on many boxes. This guide shows how to read CADR, a simple rule for sizing, and five purifiers matched to common rooms.

Sizing matters because an undersized purifier cleans the air too slowly to help, and an oversized one costs more and runs louder than you need. The coverage figures on listings are often written for one full air change per hour, which is far less demanding than the standard that allergy and smoke guidance assumes.

Below are the sizing rules, a quick chart by square footage, a table of five popular models with their published CADR numbers, and notes on noise, filters and running costs.

CADR and Room Size Explained

CADR is the number that tells you how much clean air a purifier delivers each minute. AHAM, the home appliance trade association behind the Verifide certification, tests portable air cleaners for smoke, dust and pollen and prints the three numbers and a suggested room size on the label. A bigger CADR cleans a bigger room faster.

Marketing text often uses a different figure. A listing that says a purifier covers 1,000 sq ft or more is usually describing one full air change per hour. Levoit’s own page for the Core 300-P shows both: 1,066 sq ft at one air change per hour and 222 sq ft at 4.8 air changes per hour, with a CADR of 143 CFM. The second figure is the one to compare against your room.

The Two-Thirds Rule and Air Changes per Hour

AHAM’s sizing rule says the smoke CADR should be at least two-thirds of the room’s floor area in square feet, for rooms with ceilings up to 8 feet. AHAM’s example is a 10 by 12 foot room, 120 sq ft, which needs a smoke CADR of at least 80.

The same rule works out to about five air changes per hour. You can check any purifier with the formula: air changes per hour equals CADR times 60, divided by room volume in cubic feet. The Core 300-P in a 222 sq ft room with an 8 foot ceiling gives 143 times 60 divided by 1,776, or about 4.8, matching Levoit’s own number. If your ceiling is 9 feet, multiply the required CADR by 9/8. If anyone in the house has allergies or asthma, or you want to clear smoke after cooking, aim for the top of the range rather than the bottom.

Quick Size Chart by Square Footage

These minimums are our calculation from AHAM’s two-thirds rule for 8 foot ceilings. Round up if you can.

The numbers apply to a single room with the door closed. In an open plan, treat the connected space as one room, or put one unit in each zone.

Noise, Filters and Running Costs

Fan speed is the trade-off. A purifier sized close to the minimum has to run at its top speed to hit its CADR, which is when it is loudest. Buying a size up lets you run it lower and quieter. Listings give 24 dB on sleep mode for the Levoit units, 24 to 53 dB for the Coway Mighty, 22 to 54 dB for the Airmega 250 and about 27.8 dB for the Winix 5500-2.

Filters are the running cost. Sellers list about 6 to 12 months of life for these models, so follow the manufacturer’s guidance and set a reminder. For pet homes, our guide to the best air purifier for pets compares models built for dander and odor, and if the room is a bedroom, the best air purifier for bedroom picks quiet models. Dry winter air is a separate problem; see the best humidifier for bedroom.

Our Picks by Room Size

For a bedroom up to about 215 sq ft, the Levoit Core 300-P covers it. For a bigger bedroom or living room around 350 sq ft with a wish for an app and a sensor, the Levoit Core 400S-P suits. For the same size with no app, the Coway Airmega AP-1512HH or the Winix 5500-2 meets the same rule, and the Winix has a washable carbon filter for odors. For an open-plan space of about 370 sq ft or more, the Coway Airmega 250 is the largest here. Dander also settles in carpets, so a robot vacuum for pet hair can cut how much the purifier has to handle.

When the Two-Thirds Rule Needs Adjusting

The two-thirds rule and the “up to X sq ft” labels assume a standard room. AHAM, the trade group behind CADR testing, bases its room-size ratings on an 8-foot ceiling. Three situations push you to buy bigger than the chart says.

High ceilings. A room with a 12-foot ceiling holds half again as much air as the same floor area with an 8-foot ceiling (12 divided by 8). Multiply the floor area by that ratio before you use the chart, so a 200 sq ft room with 12-foot ceilings sizes like a 300 sq ft one.

Open floor plans. Air does not stop at a doorway. If your living room flows into a kitchen and dining area, size for the connected space you actually sit in, or plan on two smaller units placed at opposite ends rather than one that is stretched to its limit.

Pets, smoke and allergy season. The chart targets typical dust and smoke. If you have a shedding dog, a cooking-heavy kitchen or a bad pollen week, the extra margin lets you run the purifier on a quiet fan setting and still keep up. A unit sized exactly to the room must run on high to meet the label, and high is where purifiers are loudest.

A quick worked example: a 280 sq ft living room with 10-foot ceilings behaves like 350 sq ft (280 x 10/8). Two-thirds of that is about 233 sq ft of CADR, so shop for a smoke CADR near 235 or higher rather than the 190 you would get from the floor area alone.