Sizing & CADR · reference
Air Purifier for a 300 Sq Ft Room: 195 CADR
for a room of 300 square feet
EPA published table · assumes an 8-foot ceiling
EPA publishes a minimum clean air delivery rate of 195 cfm for a room of 300 square feet, assuming an eight-foot ceiling. That is the whole answer for particles: pick a unit whose CADR reaches 195 or better, and the room is covered.
CADR is the only number on the box that is comparable between brands, and 195 cfm is a minimum rather than a target, a room between two published sizes takes the larger row. What the table does not cover is any question about odours, and this page will not pretend otherwise.
Why 195 cfm for 300 square feet#
The figure comes straight from the EPA's Guide to Air Cleaners in the Home: for every 100 square feet of room area, the guide publishes one minimum CADR. A room of 300 square feet lands on the 195 cfm row. The rating assumes an eight-foot ceiling, if yours is higher, EPA advises choosing a unit with a higher CADR than the table shows.
Tobacco smoke represents the smallest particles in the test, so when two units both clear 195 cfm, the tie-breaker is the smoke CADR, the higher of the three published numbers is the one to trust for fine particles.
The published table in full#
Your row is 300 → 195. The next published size up is 400 square feet at 260 cfm. If your room sits between the two, use the larger row.
| Room area (sq ft) | Minimum CADR (cfm) |
|---|---|
| 100 | 65 |
| 200 | 130 |
| 300 | 195 |
| 400 | 260 |
| 500 | 325 |
| 600 | 390 |
Suggested next step
Compare what the table asks for
Search listings for the published minimum your room needs, then check the smoke CADR on the shortlist before anything else.
What to check besides the number#
- The smoke CADR, it covers the smallest particles, which is what dust and smoke complaints are actually about.
- Dust and pollen CADR, the three test particles bracket the size range; all three should be printed on a rated unit.
- Filter availability, the purifier is bought once; the filters are bought for as long as you own it.
- Noise at the speed you will run, an oversized unit on low is quieter than an undersized one on high.
The two things the box will not tell you#
There is no published CADR for odours. CADR is defined for particles, smoke, dust and pollen. Any odour or VOC claim on a purifier sized for 300 square feet has no published minimum behind it, and this page will not manufacture one.
MERV is not a room-size rating. If a product page quotes a MERV figure as though it sizes the unit for 300 square feet, it is answering a different question, MERV grades how well a furnace filter captures particles, not how much clean air a room receives.
Questions people actually ask
Sources
- U.S. Environmental Protection Agency, Guide to Air Cleaners in the Home (2nd edition), retrieved 2026-08-30
- U.S. Environmental Protection Agency, Guide to Air Cleaners in the Home (2nd edition)
Quoted and transcribed, never paraphrased into new numbers. This site does not interpolate between published figures.
Suggested next step
One more angle before you decide
The minimum is settled, spend the rest of the decision on noise, filter cost and the smoke CADR.
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Printed from https://roomandfilter.com/sizing/air-purifier-for-a-300-square-foot-room, “Air Purifier for a 300 Sq Ft Room: 195 CADR”. Figures from U.S. Environmental Protection Agency, Guide to Air Cleaners in the Home (2nd edition), retrieved 2026-08-30. No prices are shown on this site, by policy.