If you're shopping for an air purifier, you've probably seen the term CADR everywhere. But what does it actually mean? And more importantly — what CADR number do you need for your room? Let's break it down in simple terms.
CADR stands for Clean Air Delivery Rate.
It measures how quickly an air purifier can remove specific pollutants from the air.
CADR is measured in:
The higher the CADR number, the faster the purifier cleans the air.
Important: CADR is not a single number. There are usually three ratings:
Smoke CADR is the most important because smoke particles are the smallest (and hardest to remove). When comparing purifiers, prioritize Smoke CADR.
Many brands advertise: "Covers up to 1,200 sq ft!"
But that number often assumes:
That doesn't mean effective cleaning.
CADR tells you actual cleaning speed — not marketing promises. See our best air purifiers of 2026 for models ranked by verified CADR performance.
Here's the simple rule:
Minimum CADR = 2/3 of your room size (in square feet)
Example:
Room = 300 sq ft
300 x 0.67 = ~200 CFM CADR minimum
For wildfire smoke or allergies:
CADR should equal your room size.
300 sq ft → 300 CFM CADR. For allergy-specific picks, see our best air purifiers for allergies guide.
Standard advice assumes 8-foot ceilings. If your ceiling is higher:
Example: 300 sq ft room with 10 ft ceiling: 300 x 10 / 8 = 375 sq ft equivalent. You need CADR for ~375 sq ft.
CADR determines ACH. Higher CADR means more air changes per hour, which means cleaner air faster.
For good air quality:
Minimum
4–5 ACH
Better for Allergies / Smoke
5–6+ ACH
Mostly yes — but consider:
Oversizing a purifier is usually good — you can run it on lower speed while maintaining strong performance. For quiet bedroom picks, check our best air purifier for bedroom guide.
CADR applies to particulate removal only.
HEPA Filters
Particles (dust, pollen, smoke)
Carbon Filters
Gases and odors (no CADR rating)
CADR does not measure VOC removal. To understand the difference between these filter types, read our HEPA vs Carbon Filter guide.
| Room Size | Minimum CADR | Ideal CADR (Smoke / Allergies) |
|---|---|---|
| 150 sq ft | 100 CFM | 150 CFM |
| 300 sq ft | 200 CFM | 300 CFM |
| 500 sq ft | 335 CFM | 500 CFM |
| 800 sq ft | 535 CFM | 800 CFM |
Always check the actual CADR rating instead of relying on room size claims. Our best air purifiers of 2026 guide lists verified CADR numbers for every model.
CADR tells you how fast an air purifier cleans the air.
If you remember one thing:
CADR should be at least 2/3 of your room size.
For smoke or allergies, match CADR to room size.
If you want high-performance models that meet proper CADR standards, see our updated rankings in Best Air Purifiers 2026.
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