Air Purifier CADR Ratings Complete Guide 2026: Understanding Clean Air Delivery Rate
After spending years testing air purifiers and helping readers choose the right models, I’ve noticed one specification confuses people more than any other: CADR.
CADR stands for Clean Air Delivery Rate, and it’s the only standardized rating that tells you how effectively an air purifier cleans your air.
Understanding CADR ratings means the difference between buying an air purifier that actually works and wasting money on a device that can’t handle your room.
What is CADR?
CADR (Clean Air Delivery Rate) measures how effectively an air purifier removes smoke, dust, and pollen from the air.
Higher CADR numbers mean faster, more effective cleaning.
The rating is expressed in cubic feet per minute (CFM) and considers both airflow and filtration efficiency.
CADR (Clean Air Delivery Rate): A standardized measurement developed by AHAM that indicates how effectively an air purifier removes specific particle sizes (smoke, dust, pollen) from the air, expressed in cubic feet per minute.
CADR testing follows the AC-1 standard established by the Association of Home Appliance Manufacturers (AHAM).
This standardized testing allows you to compare different air purifiers objectively.
Each air purifier receives three separate CADR ratings for different particle types.
The Three CADR Ratings Explained
Every certified air purifier has three CADR ratings, each measuring effectiveness against different particle sizes.
| CADR Type | Particle Size | Real-World Examples | Who Needs It Most |
|---|---|---|---|
| Smoke CADR | 0.09-1.0 microns | Wildfire smoke, cigarette smoke, cooking fumes | Smoke exposure, urban areas |
| Dust CADR | 0.5-3 microns | Dust mites, pet dander, mold spores | Allergy sufferers, pet owners |
| Pollen CADR | 5-11 microns | Tree pollen, grass pollen, ragweed | Seasonal allergy sufferers |
The smoke CADR is typically the lowest of the three ratings because fine particles are hardest to capture.
For general air cleaning, the smoke CADR matters most since it represents the smallest, most difficult particles to remove.
If you’re dealing with smoke from wildfires or cigarettes, check out our guide to the best air purifiers for smoke removal for models with high smoke CADR ratings.
Pollen CADR is usually the highest rating since larger particles are easier to trap.
How CADR is Calculated?
CADR is calculated by multiplying an air purifier’s airflow by its filtration efficiency.
Formula: CADR = Airflow (CFM) x Filtration Efficiency (%)
For example, a purifier with 300 CFM airflow and 80% filter efficiency has a CADR of 240.
The testing happens in a controlled 1,008 cubic foot room with the purifier on maximum speed.
- Step 1: Measure the purifier’s airflow in cubic feet per minute
- Step 2: Test filter efficiency with specific particle sizes
- Step 3: Multiply airflow by efficiency percentage
- Step 4: Verify results through independent AHAM testing
AHAM-verified models undergo third-party testing to ensure advertised CADR ratings are accurate.
I’ve tested dozens of models and found AHAM verification is the most reliable indicator of real performance.
The 2/3 Rule: Room Sizing Made Simple
The 2/3 rule is AHAM’s guideline for choosing the right CADR for your room.
Your air purifier’s smoke CADR should be at least two-thirds of your room’s square footage.
This calculation assumes a standard 8-foot ceiling height.
The 2/3 Rule Formula: Minimum CADR = Room Square Footage x 0.67
For a 300 sq ft bedroom, you need a CADR of at least 200 (300 x 0.67 = 201).
Going higher than the minimum gives you faster air cleaning and more air changes per hour.
I recommend rounding up when choosing between models.
Room Size to CADR Quick Reference
Use this table to find the CADR you need for your space.
| Room Size | Minimum CADR (2/3 Rule) | Recommended CADR | Air Changes per Hour |
|---|---|---|---|
| 100 sq ft | 67 | 100+ | 5+ |
| 150 sq ft | 100 | 150+ | 5+ |
| 200 sq ft | 134 | 200+ | 4-5 |
| 300 sq ft | 200 | 250+ | 4-5 |
| 400 sq ft | 268 | 300+ | 3-4 |
| 500 sq ft | 335 | 400+ | 3-4 |
| 600 sq ft | 400 | 450+ | 3 |
| 800 sq ft | 536 | 600+ | 2-3 |
| 1000 sq ft | 670 | 700+ | 2-3 |
For large spaces like basements and open-concept areas, you may need multiple units or a commercial-grade purifier.
Our guide to large room air purification covers options for spaces over 500 sq ft.
High Ceiling Adjustments
The standard 2/3 rule assumes 8-foot ceilings.
If your ceilings are higher, increase your CADR requirement proportionally.
For 10-foot ceilings, multiply the minimum CADR by 1.25.
For 12-foot ceilings, multiply by 1.5.
Using Multiple Units
Multiple smaller units can outperform one large unit in the same space.
Two units with CADR 200 each provide better coverage than one unit with CADR 400.
Strategic placement allows for more even air distribution throughout the room.
Advanced CADR Topics
PM2.5 CADR: The New 2026 Standard
PM2.5 CADR is a new metric introduced in 2026 that measures removal of particles smaller than 2.5 microns.
This rating roughly averages the smoke and dust CADR ratings.
PM2.5 particles are the most harmful to human health because they penetrate deep into lungs.
Energy Star 3.0, launching October 2026, uses PM2.5 CADR instead of the traditional three ratings.
CADR vs CFM: Understanding the Difference
CFM measures raw airflow while CADR measures clean air delivery.
| Metric | What It Measures | How Used | Limitations |
|---|---|---|---|
| CADR | Clean air output (CFM x efficiency) | Comparing purifier performance | Doesn’t measure gases or VOCs |
| CFM | Raw airflow volume | Fan capacity calculation | Doesn’t account for filter efficiency |
| Airflow | General movement of air | Circulation assessment | Not standardized |
A high CFM with a poor filter still gives low CADR.
Always look at CADR, not CFM, when comparing models.
CADR Limitations: What It Doesn’t Measure
CADR doesn’t measure noise level, which matters for bedrooms and offices.
It also doesn’t account for gas removal, VOCs, or odors.
If noise is a priority for you, explore our guide to quiet operation models.
CADR ratings also assume a clean filter and maximum fan speed.
Real-world performance is typically lower than lab-tested CADR.
Filter Degradation Over Time
As filters load with particles, airflow decreases and CADR drops.
A dirty filter can reduce effective CADR by 30-50%.
Replace filters according to manufacturer guidelines to maintain performance.
I’ve seen CADR effectively halve after 6 months of heavy use in dusty environments.
Using CADR to Choose an Air Purifier
Look for AHAM Verification
AHAM-verified models display the certification seal on packaging and listings.
Verified models are randomly retested to ensure ongoing accuracy.
The AHAM database lets you look up specific model ratings.
Energy Star Certification
Energy Star certification ensures efficiency without sacrificing performance.
The new Energy Star 3.0 standard uses Integrated Energy Factor (IEF) based on PM2.5 CADR per watt.
Certified models cost less to run while maintaining strong CADR ratings.
Avoid Red Flags
- Missing CADR ratings: Legitimate brands publish all three ratings
- Suspiciously high numbers: Some foreign brands use m3/h instead of CFM (multiply by 0.59 to convert)
- No AHAM verification: Self-reported ratings aren’t trustworthy
- Only one rating listed: Should have separate smoke, dust, and pollen CADR
Compare Models by CADR
Use CADR to compare similar models directly.
When comparing air purifier performance, match CADR ratings against your room size.
Slightly higher CADR justifies a moderate price increase for better coverage.
Don’t pay significantly more for marginally higher CADR unless you have a larger room.
Frequently Asked Questions
What is a good CADR for air purifier?
A good CADR rating follows the 2/3 rule: multiply your room’s square footage by 0.67. For a 300 sq ft room, look for a CADR of at least 200. Going higher provides faster cleaning and more air changes per hour.
How much CADR is good for an air purifier?
The minimum CADR should be two-thirds of your room’s square footage. A 200 sq ft room needs CADR 134 minimum, but CADR 200+ is recommended for optimal performance. Larger spaces over 500 sq ft may require multiple units.
Is 200 CADR good?
Yes, 200 CADR is good and adequate for rooms up to 300 sq ft using the 2/3 rule. It’s a common rating for medium-sized bedroom air purifiers and provides 4-5 air changes per hour in typical applications.
Is 300 CADR good?
Yes, 300 CADR is excellent and suitable for rooms up to 450 sq ft. This rating is found in larger residential air purifiers and provides strong performance for living rooms, open kitchens, or master bedrooms.
Is higher CADR always better?
Not necessarily. Higher CADR provides faster cleaning but may be overkill for small rooms, increase energy costs, and create more noise. Match CADR to your room size using the 2/3 rule for the best balance of performance and practicality.
What is the 2/3 rule for CADR?
The 2/3 rule states that your air purifier’s smoke CADR should be at least two-thirds (66.7%) of your room’s square footage. For example, a 400 sq ft room needs a minimum CADR of 268. This guideline assumes standard 8-foot ceilings.
What’s the difference between CADR and CFM?
CFM measures raw airflow volume while CADR measures clean air delivery accounting for filter efficiency. A purifier with high CFM but poor filtration has low CADR. CADR is the better metric for comparing actual cleaning performance between models.
Key Takeaways
- CADR measures effectiveness: Higher numbers mean faster, more complete air cleaning
- Follow the 2/3 rule: Minimum CADR = room square footage x 0.67
- Smoke CADR matters most: It’s the hardest rating to achieve and indicates overall performance
- Look for AHAM verification: Third-party testing ensures accurate ratings
- Consider your ceiling height: Adjust CADR requirements for rooms taller than 8 feet
- Maintain your filters: Dirty filters reduce effective CADR significantly
Understanding CADR takes the guesswork out of choosing an air purifier.
Use the 2/3 rule, look for AHAM verification, and match the smoke CADR to your room size for reliable results.
