What size air purifier do I need for my room?

Match the CADR to the room: for an 8-foot ceiling, a room needs roughly 2/3 of its square footage in CADR (CFM) for 4.8 air changes per hour. So a 200 sq ft bedroom needs ~135-200 CFM, a 300 sq ft living room needs ~200-300 CFM, and a 500 sq ft space needs ~330-500 CFM. Check the chart in this article for exact numbers.

What CADR do I need for a 200 sq ft room?

A 200 sq ft room with 8-foot ceilings needs about 135-200 CFM of CADR. That covers a bedroom, small office, or nursery. The Levoit Vital 200S (200 CFM) and Coway Airmega 150 (160 CFM) are both in the right range.

What CADR do I need for a 300 sq ft room?

A 300 sq ft room needs about 200-300 CFM of CADR. That's most living rooms and master bedrooms. The Coway AP-1512HH (233 CFM), Winix 5500-2 (232 CFM), and Levoit Core 400S (250 CFM) all fit.

What CADR do I need for a 500 sq ft room?

A 500 sq ft open-plan space needs about 330-500 CFM. The Levoit Core 600S (400 CFM), Blueair Blue Pure 211+ (350 CFM), and Coway Airmega 400 (350 CFM) are the right class. For 600+ sq ft, look at the Medify MA-112 (490 CFM).

Is bigger CADR always better?

Bigger is better up to a point — oversizing by 20-30% gives you faster cleaning and quieter operation (you can run a big unit on low). But a massively oversized unit costs more, and on high it can create drafty airflow. The sweet spot is 1-1.5x the recommended CADR for your room.

Room Size to Air Purifier Chart: What CADR Do You Actually Need?

Buying an air purifier without matching it to your room size is the #1 mistake — and it explains most “my purifier doesn’t seem to do anything” complaints. A unit that’s too small can run forever without meaningfully cleaning the air. Here’s the exact chart, the math behind it, and the units that fit every room size.

🧰 Interactive Tools

📏Room Size CalculatorEnter your room, get the exact CADR→ 🧮CADR CalculatorReverse-match a unit to your room→

The Room Size Chart (8-Foot Ceilings)

Measuring a room with a tape measure

Room size	CADR needed (min)	Recommended range	Example rooms
100 sq ft	67 CFM	70-110 CFM	Small bedroom, nursery, office nook
150 sq ft	100 CFM	100-160 CFM	Bedroom, small office
200 sq ft	135 CFM	135-200 CFM	Standard bedroom, dorm
250 sq ft	167 CFM	170-250 CFM	Large bedroom, small living room
300 sq ft	200 CFM	200-300 CFM	Living room, master bedroom
400 sq ft	267 CFM	270-400 CFM	Open living/dining, large master
500 sq ft	333 CFM	330-500 CFM	Open-plan apartment, loft
750 sq ft	500 CFM	500-700 CFM	Large open-plan, studio+
1,000 sq ft	667 CFM	650-900 CFM	Whole apartment, basement

The Math (So You Can Do It Yourself)

The formula behind the chart is simple:

CADR needed (CFM) = Room area (sq ft) × 2/3

That’s based on AHAM’s recommendation of 4.8 air changes per hour for effective air cleaning. For allergy/asthma use, aim for 5 ACH (the × 2/3 rule covers it); for light maintenance, 4 ACH is acceptable (multiply area by 0.55 instead).

Ceiling height matters: for 10-foot ceilings, add ~25% to the CADR number. For 9-foot ceilings, add ~12%.

Which Unit Fits Your Room?

Small Rooms (100-200 sq ft) — Levoit Core 300 ($99)

130 CFM covers up to ~195 sq ft at 4.8 ACH. True HEPA, quiet (24 dB on low), and filters cost about $30/year. The value pick for bedrooms and dorms.

Medium Rooms (200-300 sq ft) — Levoit Core 600S ($299)

400 CFM — that’s actually sized for up to 600 sq ft, which means in a 300 sq ft room it cleans on low, quietly. True HEPA, app control, and it’s the unit we recommend when you want headroom and silence rather than the bare minimum.

Large Rooms / Open Plans (400-750 sq ft) — Medify Air MA-112 ($449)

490 CFM, True HEPA, and a washable pre-filter. It’s one of the few units genuinely sized for 700+ sq ft, with a medical-grade filter rating (H13). The right call for open-plan apartments and basements where one unit needs to cover a lot of ground.

Not Sure? Use the Tools

Every room is different — ceiling height, open doorways, and layout all shift the number. The room size calculator does the exact math for your space, and the CADR calculator lets you check a unit you already own. Two minutes with either beats guessing.

The Bottom Line

Match the CADR to the room: area × 2/3 = minimum CFM. Small rooms get by with 100-200 CFM units; medium rooms need 200-300; large open plans need 350+. Oversizing by a third is fine and buys you quieter operation — undersizing is the mistake that makes purifiers feel useless. When in doubt, use the calculator and buy the bigger unit.