You’re shopping for an air purifier. You’ve got three tabs open, comparing specs, and every single one lists something called “CADR.”
One says 200. Another claims 350. A third boasts 400+ like it’s a badge of honor.
But what does any of that actually mean for your bedroom? Your living room? Your life?
I spent an embarrassing amount of time figuring this out, and honestly, most product descriptions don’t help. They throw numbers at you and assume you understand. Spoiler: most people don’t, and manufacturers count on that.
Let’s fix that right now.
What CADR Actually Stands For
CADR means Clean Air Delivery Rate. It’s measured by the Association of Home Appliance Manufacturers (AHAM), and it tells you how much filtered air an air purifier can deliver per minute.
Think of it like this: if your air purifier was a water filter, CADR would tell you how many gallons of clean water it produces per minute. Higher numbers mean more clean air, faster.
The number itself represents cubic feet per minute (CFM) of filtered air. A CADR of 300 means the unit delivers 300 cubic feet of cleaned air every minute.
Simple enough, right? Except there’s more to it.
The Three CADR Numbers You’ll See
Here’s where it gets interesting. Most air purifiers don’t list one CADR—they list three:
Smoke CADR – Measures particles 0.09-1.0 microns (the smallest stuff)
Dust CADR – Measures particles 0.5-3.0 microns (medium-sized particles)
Pollen CADR – Measures particles 5.0-11.0 microns (the biggest particles)
Why three numbers? Because particle size matters tremendously for filtration efficiency.
Smoke particles are tiny. They’re the hardest to capture. If an air purifier has a high smoke CADR, it’s doing serious work at the microscopic level. That’s why smoke CADR is usually the lowest of the three numbers.
Pollen particles are huge by comparison. Easier to catch. That’s why pollen CADR is typically the highest.
When manufacturers advertise their CADR, guess which number they highlight? Yeah, the pollen one. The biggest, most impressive number that tells you the least about real-world performance.
What Actually Matters for Your Home
Here’s the part nobody explains well: CADR only matters relative to your room size.
You need to match the CADR to the space you’re trying to clean. Too low? The air purifier can’t keep up. Too high? You’re overpaying for capacity you don’t need.
The standard recommendation is to find a CADR that’s at least two-thirds of your room’s square footage. Want faster air cleaning? Go higher.
Let’s make this concrete:
Small bedroom (100 sq ft): Minimum CADR of 65-70
Medium bedroom (150 sq ft): Minimum CADR of 100
Large bedroom (200 sq ft): Minimum CADR of 130-140
Living room (300 sq ft): Minimum CADR of 200
Large open space (400 sq ft): Minimum CADR of 265+
These are minimums. They’ll give you decent filtration with about 4 air changes per hour—the standard for maintaining air quality.
Want cleaner air faster? Double those numbers. That gets you closer to 8 air changes per hour, which is what hospitals aim for.
The Air Changes Per Hour Connection
This is crucial and almost never explained properly.
Air changes per hour (ACH) tells you how many times an air purifier cycles through all the air in your room. Most air purifiers are rated for either 4 or 5 ACH when they advertise their “recommended room size.”
Here’s the formula that actually matters:
CADR × 60 minutes ÷ Room Volume = ACH
Your room volume is length × width × height in cubic feet.
Example: You’ve got a 12×15 room with 8-foot ceilings. That’s 1,440 cubic feet.
Your air purifier has a CADR of 200.
200 × 60 = 12,000
12,000 ÷ 1,440 = 8.3 ACH
That’s actually excellent. You’re getting 8 complete air changes every hour.
Most people never do this math. They just see “good for rooms up to 300 sq ft” and trust it.
Why Manufacturer Room Size Claims Are Misleading
When a box says “ideal for rooms up to 500 square feet,” that’s based on one specific assumption: you’re okay with the absolute minimum effective filtration.
They’re calculating at the bare minimum AHAM standard—usually around 2-3 ACH. That technically filters the air, but slowly.
If you have allergies, pets, or live in a polluted area, you need better than “technically works.” You want 5-6 ACH minimum, ideally more.
So take those room size claims and cut them in half for real-world performance.
A purifier rated for 500 sq ft? It’ll actually perform well in a 250 sq ft room.
The Marketing Tricks Nobody Tells You About
Trick #1: Highlighting pollen CADR only
Remember those three CADR ratings? Companies love showing you the pollen number (the highest) while burying the smoke CADR (the most important for actual air quality).
Always check the smoke CADR. That’s your real performance indicator.
Trick #2: Maximum fan speed ratings
CADR is measured at the highest fan speed setting. That speed is often loud—like “can’t watch TV” loud.
You’ll probably run your purifier on medium most of the time. But there’s no standard CADR rating for medium speed. You’re flying blind on actual daily performance.
Trick #3: Energy Star vs CADR
Some units market their Energy Star rating prominently but have mediocre CADR. Energy efficiency is great, but not if the thing barely cleans your air.
You can have both—just don’t let the Energy Star badge distract you from checking the CADR.
What CADR Doesn’t Tell You
CADR is useful, but it’s not the whole story:
It doesn’t measure noise levels. A 300 CADR unit running at jet-engine volume isn’t practical for a bedroom.
It doesn’t account for filter quality. CADR assumes the filter is working optimally. A cheap filter degrades faster, and CADR drops with it.
It doesn’t test for gases or odors. CADR only measures particle removal. VOCs, formaldehyde, cooking smells? Not covered.
It doesn’t reflect real-world conditions. CADR is tested in controlled lab settings. Your room has furniture, air currents, doors opening and closing—all of which affect actual performance.
It doesn’t guarantee even distribution. High CADR doesn’t mean clean air reaches every corner of your room.
The CADR Number You Actually Need
Stop fixating on the highest CADR you can afford. Start with your actual room size and what you’re trying to achieve.
For basic air quality maintenance: Room square footage × 0.67 = minimum CADR
For allergies or asthma: Room square footage × 1.0 = target CADR
For heavy pollution or smoking: Room square footage × 1.5 = target CADR
A 200 sq ft bedroom with moderate needs? You want a CADR around 200.
Got pets and allergies in that same room? Aim for 250-300.
More isn’t always better if it means you never run the unit because it’s too loud or uses too much energy.
How to Actually Use CADR When Shopping
Step 1: Measure your room. Length × width = square footage.
Step 2: Look for CADR ratings in your target range (use the formulas above).
Step 3: Check the smoke CADR specifically, not just the pollen number.
Step 4: Read reviews about noise levels at different fan speeds. CADR means nothing if you can’t tolerate running the unit.
Step 5: Verify the AHAM seal. This means the CADR was independently tested, not self-reported by the manufacturer.
Step 6: Calculate the actual ACH you’ll get. Don’t trust the “room size” claims on the box.
The Bottom Line
CADR is one of the few standardized, testable metrics in the air purifier world. That makes it valuable—way more useful than vague claims about “99.97% filtration” or “medical grade HEPA.”
But it’s a starting point, not the finish line.
A high CADR in a room that’s too large won’t help you. A perfect CADR match on a unit you can’t run on high speed won’t help you either.
Use CADR as your baseline filter. Then factor in noise, energy use, filter costs, and actual room conditions.
Numbers matter, but only when you know what they mean and how to apply them to your actual life.
Now you do.
Still confused about CADR for your specific situation? Drop your room size and what you’re trying to solve in the comments. We’ll help you figure out what you actually need.