Filters & Ratings · explainer
What Is CADR, and Does It Matter?
for a 100 sq ft room, the smallest published row
The table climbs to 390 cfm at 600 sq ft.
CADR appears on every box in this category, usually as the largest number on the front. It is the one figure worth reading first, because it is the only one measured the same way by every brand that publishes it.
Here is what CADR actually measures, where the published minimums come from, and, since this site is built on the distinction, what it does not measure.
What CADR actually measures#
CADR stands for clean air delivery rate. It is the volume of filtered air a unit delivers, measured in cubic feet per minute. A unit with a CADR of 65 delivers 65 cubic feet of cleaned air per minute while running at the test speed.
It is measured in a standard test for three particle types: dust, pollen and tobacco smoke. That is why the box usually carries three CADR numbers rather than one.
The three numbers, and the one to watch#
The three test particles are not equally fine. Tobacco smoke is the smallest of the three, so the smoke CADR is the number that tells you how the unit copes with the finest particles.
EPA's guidance puts it plainly: to remove small particles, choose a portable air cleaner with a high CADR for tobacco smoke. Dust and pollen figures matter too, but smoke is where weak units are exposed.
The published minimums#
EPA publishes a minimum CADR for each room area, calculated on an eight-foot ceiling. The table is published in 100 sq ft steps and stops at 600 sq ft:
| 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.
Does it matter?#
Yes, more than anything else printed on the box. CADR is the only number that is comparable between brands, because every manufacturer that quotes it uses the same test.
Everything else on the packaging is a claim. CADR is a measurement. Room coverage claims, star ratings and "powerful" adjectives are all downstream of it, or unrelated to it.
When you are ready to compare units, start with the smoke CADR for your room size and work outward: compare HEPA air purifiers on their published CADR.
What to check on the box#
- A CADR figure at all. If a box omits it, the omission is the information.
- The tobacco-smoke CADR specifically, if the three numbers are printed separately.
- A number above the published minimum for your room area, rounded up, never down.
- Whether the coverage claim on the front matches the CADR or quietly stretches past it.
- An eight-foot ceiling assumption. Taller rooms need more than the table row.
Questions people actually ask
Sources
- U.S. Environmental Protection Agency, Guide to Air Cleaners in the Home (2nd edition), retrieved 2026-08-30
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/filters/what-is-cadr, “What Is CADR, and Does It Matter?”. 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.