CADR is the one number that predicts whether a purifier can keep up. Tell the calculator the room and the problem, and it does the AHAM math and suggests a fit.
Multiply your floor area by two-thirds to get the minimum smoke CADR, then scale by ceiling height divided by 8. A 300 sq ft room with 8 ft ceilings needs 200 cfm. For smoke, or if it runs while you sleep, add about 50%, which makes 300 cfm. The calculator below does this and suggests a purifier.
| Room (8 ft ceiling) | Minimum smoke CADR | For smoke or sleep |
|---|---|---|
| 120 sq ft bedroom | 80 cfm | 120 cfm |
| 200 sq ft bedroom | 135 cfm | 200 cfm |
| 300 sq ft living room | 200 cfm | 300 cfm |
| 500 sq ft open kitchen | 335 cfm | 500 cfm |
| 800 sq ft open plan | 535 cfm | 800 cfm |
Many boxes quote the area a purifier can clean once an hour. AHAM’s room size assumes about 4.8 air changes an hour, which is what you want for allergies or smoke. Divide a once-an-hour claim by about five.
Example: a box that says 1,000 sq ft once an hour is closer to 210 sq ft at 4.8 air changes.AHAM’s rule assumes 8 ft ceilings. Scale by your height divided by 8: a 10 ft ceiling needs 25% more CADR, a 12 ft ceiling 50% more.
12 ft vaulted: a 300 sq ft room needs 300 cfm instead of 200.One per closed room you care about. Open rooms joined by wide doorways can share, but add the areas together and check the combined CADR.
CADRs add: two units at 141 cfm give 282 cfm, enough for about 420 sq ft by the two-thirds rule.These questions come from Bing searches on this topic and from what testers measure. We summarize; we don’t run our own lab.
Five quick choices. Nothing is sent anywhere.
For your room you need at least
Room sizes use AHAM’s 4.8 air changes an hour. Size up one row if it runs while you sleep.
| Room it suits | Pick | Why |
|---|---|---|
| Up to 110 sq ft | Honeywell HPA125 | Best for a small bedroom or dorm |
| Up to 140 sq ft | Blueair Mini Restful | Best for nightstands and nurseries |
| Up to 220 sq ft | Levoit Core 300S-P | Best under $150 |
| Up to 364 sq ft, no ionizer | Coway 200M | Best filter-only pick for medium rooms |
| Up to 372 sq ft | Coway Mighty2 | Best for most rooms |
| Up to 392 sq ft | Winix 5510 | Best value with a real carbon filter |
| Up to 549 sq ft | Levoit EverestAir-P | Best for smells, with smart features |
| Up to 606 sq ft | Levoit Core 600S-P | Best big-room value |
| Up to 879 sq ft | Coway ProX | Best for open plans and wildfire smoke |
Clean air delivery rate: the cubic feet of filtered air per minute a purifier delivers on high, measured for smoke, dust and pollen under AHAM’s standard.
AHAM’s guideline that a purifier’s smoke CADR should be at least two-thirds of the room’s floor area in square feet, assuming 8 ft ceilings.
How many times an hour the purifier filters the room’s full volume. AHAM’s room sizes assume about 4.8, roughly once every 12.5 minutes.
Smoke. Smoke particles are the smallest and hardest to remove, so the smoke CADR is usually the lowest and the safest number to size by.
Yes. Add up the connected areas, choose the tallest ceiling, and consider splitting the target between two purifiers.
If it is an AHAM room size at 4.8 air changes, divide by 1.55 to get the CADR. If it is a once-an-hour figure, divide by about five first.