Sizing & CADR · reference
Why "Covers 1,500 sq ft" Means Very Little
Beyond that, no EPA minimum exists
A "covers 1,500 sq ft" claim has no published minimum behind it.
Somewhere on the box it says the unit "covers 1,500 square feet". That number is not standardised. There is no single test behind it, no stated set of room assumptions, and no way for you to check it. CADR, clean air delivery rate, is the opposite: one figure, one test, one unit of delivery.
The United States Environmental Protection Agency publishes a minimum CADR for each room size. That table is the whole basis of this site, and it is reproduced below. Everything else a manufacturer says about coverage is a claim; this is a floor you can verify.
Two numbers, two different jobs#
A coverage claim is a marketing number. It assumes a ceiling height, a fan speed, an air-change target and a room you cannot inspect. Change any assumption and the claim quietly changes with it. Two brands can put "covers 500 sq ft" on boxes that deliver very different amounts of clean air.
CADR is a delivery rate, measured in cubic feet per minute. It says how much filtered air a unit delivers, and it is the figure EPA uses when it tells you how to size a portable air cleaner. It is comparable between brands in a way a coverage claim never will be.
The published minimum, at a glance#
EPA publishes one minimum CADR for each room area, calculated on an eight-foot ceiling. This is the complete table:
| Room area (sq ft) | Minimum CADR (cfm) |
|---|---|
| 100 | 65 |
| 200 | 130 |
| 300 | 195 |
| 400 | 260 |
| 500 | 325 |
| 600 | 390 |
What "covers 1,500 sq ft" would have to mean#
A claim of 1,500 square feet reaches two and a half times past the largest published row. There is no EPA minimum for a room that size, and nothing on the box tells you which assumptions were used to reach the figure. compare large-room air purifiers on Amazon and you will find similar claims attached to very different CADR numbers.
That is the whole point. The coverage claim cannot be checked. The CADR can: find it on the label, find your room's row in the table, and compare.
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.
How to sanity-check any coverage claim#
- 1Find the CADR on the label or spec sheet. If a unit lists a coverage area but no CADR, you cannot size it at all.
- 2Measure your room's floor area and find the published row. Between two rows, take the larger, CADR is a minimum, so rounding up is always safe and rounding down is always wrong.
- 3Check the tobacco-smoke CADR as well as dust and pollen. Tobacco smoke represents the smallest particles, which is where weak units fall short first.
- 4Treat the coverage claim as decoration. If it disagrees with the CADR arithmetic, believe the CADR.
The verdict#
Buy on CADR. Sanity-check the coverage claim against your room, if you bother with it at all. A unit whose CADR meets the published minimum for your room is sized correctly; a unit with an impressive coverage figure and a missing or mediocre CADR is a guess wearing a spec sheet.
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/sizing/cadr-vs-coverage-area, “Why "Covers 1,500 sq ft" Means Very Little”. 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.