What Is a CADR Rating? A Simple Guide to Choosing Your Air Purifier

If you’ve spent more than five minutes shopping for an air purifier, your head is probably spinning. The market is a jungle of technical jargon: “True HEPA,” “PECO,” “ionizers,” “CFM,” “ACH“… it’s intentionally confusing.

When I first started seriously researching air quality, I just wanted one, simple, independent number that could cut through the marketing hype and tell me: “Does this thing actually work, and is it powerful enough for my room?”

That number is the CADR rating.

In short, CADR is the single most important, third-party-verified “apples-to-apples” metric for comparing the power and performance of different air purifiers. This guide will teach you what it means, how to use it, and—most importantly—what its limitations are.

Key Takeaways

• What CADR Is: CADR stands for Clean Air Delivery Rate. It’s a measure of an air purifier’s cleaning speed—how much clean air it delivers in cubic feet per minute (CFM).
• The “2/3 Rule”: This is the simple formula you need. Your purifier’s Smoke CADR rating should be at least two-thirds (2/3) of your room’s area in square feet (e.g., a 150 sq. ft. room needs a 100 CADR).
• The Trust Signal: Always look for the “AHAM Verifide®” seal. This proves the CADR numbers have been independently tested and are not just a marketing claim.
• The Main Limitation: CADR only measures particles (smoke, dust, pollen). It does NOT measure the removal of gases, chemicals (VOCs), or odors.

What Is CADR in Simple Terms? (The 1-Minute Answer)

So, what does CADR mean on an air purifier?

Think of your air purifier as a small “room cleaner” and its CADR rating as its cleaning speed.

It answers one simple question: “How many buckets of clean air can this machine pour back into my room every single minute?”

It’s measured in CFM (Cubic Feet per Minute). A purifier with a CADR of 200 means it can deliver 200 cubic feet of 100% clean air every minute. A higher number means a faster, more powerful machine that can clean a larger room.

Simple Analogy: Imagine your room is a large, dirty swimming pool. The CADR rating is like knowing how many gallons of fresh, filtered water the pool pump can pour back in per minute. A pump with a high GPM (gallons per minute) will clean the pool much faster. A high CADR does the same for your air.

Why Are There Three Numbers? (Smoke, Dust, and Pollen)

When you look at the official AHAM seal, you’ll see not one, but three CADR numbers. This is because what is in air purifiers are filters, and not all airborne particles are the same size or as easy to catch.

The test measures the purifier’s “cleaning speed” against three specific pollutants:

1. Smoke: These are the smallest, finest particles (0.09 – 1.0 microns).
2. Dust: These are mid-sized particles (0.5 – 3.0 microns) like lint, dander, and dust mite allergens.
3. Pollen: These are the largest particles (5.0 – 11.0 microns), like seasonal allergens.

Which CADR Number Is Most Important?

For almost everyone, the Smoke CADR is the most critical number to look at.

These tiny particles (often called PM2.5) are the most dangerous to our health because they can get deep into our lungs and even enter the bloodstream. This rating also serves as the best benchmark for a purifier’s ability to handle other fine particulates, like wildfire smoke, smog, and vehicle exhaust.

This is why the standard room-size calculation is based on the Smoke rating.

How to Use CADR to Pick the Right Air Purifier for Your Room

This is the practical part. Forget complex math; you only need one simple, industry-standard rule to find the right-sized purifier.

The “2/3 Rule” (The AHAM Standard)

This is the golden rule for matching a purifier to a room.

The Rule: Your air purifier’s Smoke CADR should be at least two-thirds (2/3) of your room’s area in square feet.

Here is your simple CADR calculator process:

1. Measure Your Room: Find the square footage (Length x Width).
   • *Example: A 10-foot by 15-foot bedroom is 150 sq. ft.
2. Calculate 2/3 of That Area: Multiply your square footage by 0.66.
   • *Example: 150 sq. ft. x 0.66 = 99
3. Find Your Number: You need a purifier with a Smoke CADR of at least 100 (it’s okay to round up!) for that room.

When to Use a Stricter “1:1 Rule”

The 2/3 Rule is great for general air quality maintenance. But if you have specific, heavy-duty needs, you should be more aggressive.

• Who needs this? Anyone with severe allergies, asthma, or high-pollution concerns (like living near a highway or in a wildfire-prone area).
• The Rule: Aim for a Smoke CADR that is equal to your room’s square footage.
• Example: For that same 150 sq. ft. room, you would want a Smoke CADR of at least 150.

This ensures the air is being cleaned much faster and more frequently, which is what you need to get relief from acute symptoms or pollution events.

Who Sets This Standard? Why You Can Trust CADR

In a market full of hyped-up marketing claims, the CADR rating is your one source of truth. It’s not a number a brand invents—it’s the result of a standardized test.

• AHAM (Association of Home Appliance Manufacturers): This is the industry group that developed and manages the standard (officially called ANSI/AHAM AC-1).
• ANSI (American National Standards Institute): This is the independent, non-profit organization that accredits the testing standard, ensuring it’s fair, uniform, and repeatable.
• EPA (Environmental Protection Agency): The U.S. government doesn’t test purifiers, but it officially recommends that consumers use the CADR rating to select the right product.

What to Look For: The “AHAM Verifide®” Seal

This is your proof.

When you see this blue seal on a box, it means the manufacturer has voluntarily submitted its product to an independent, third-party lab. That lab has tested the unit and confirmed that its CADR claims for Smoke, Dust, and Pollen are 100% accurate.

My rule: If a purifier makes big claims but doesn’t have the AHAM Verifide® seal, I ignore it.

CADR Is Just the Starting Point: 3 Things It Doesn’t Tell You

This is the most important part of my guide. I’m a firm believer in CADR, but as an expert, I have to be honest: a high CADR tells you a machine is powerful, but it doesn’t tell you the whole story.

A smart purchase means asking the questions what is cadr rating of air purifier not telling you.

1. It Does NOT Measure Gases, Chemicals (VOCs), or Odors

This is the single biggest misconception. The CADR test only uses solid particles.

It tells you nothing about the purifier’s ability to remove:

• VOCs (Volatile Organic Compounds) from new furniture, paint, or mattresses.
• Chemicals from cleaning supplies or smoke.
• Household odors from cooking, pets, or garbage.

What to look for instead: For these pollutants, you need a different kind of filter: Activated Carbon. If odors and chemicals are your main concern, you must look for a purifier with a substantial carbon filter (ideally several pounds of it), a feature that is not measured by or reflected in the CADR score. For a complete breakdown of purifiers that excel at this, you can read my guide to the best air purifiers for VOCs and chemical removal.

2. It Does NOT Measure “Quiet” Performance

This one is a sneaky “gotcha” for many buyers.

The official CADR rating is only measured at the air purifier’s absolute highest, loudest fan speed.

Nobody (and I mean nobody) runs a purifier on “tornado” mode in their bedroom while trying to sleep. You will most likely run your unit on a low or medium setting for comfort.

At these quieter, lower speeds, the effective CADR (and cleaning power) will be significantly lower than the number on the box.

How to solve this: This is why I always recommend “oversizing” your purifier. Buy a unit that is rated for a much larger room than you have. For example, put a purifier with a 250 CADR (rated for ~375 sq. ft.) in your 150 sq. ft. bedroom. This way, you can run it on its medium or low setting, and it will still have more than enough power to clean your room quietly and effectively.

3. It Is NOT the Same as a HEPA Filter

This is the most common point of confusion.

• HEPA is a filter quality standard. “True HEPA” means the filter itself is certified to capture 99.97% of 0.3-micron particles.
• CADR is a system performance rating. It measures how much clean air the entire machine (fan + filter) actually produces.

Why this matters: A company can put a “True HEPA” filter in a machine with a weak, asthmatic fan or a poorly designed case that lets dirty air leak around the filter. That unit would have a terrible CADR score.

Always look for both: a True HEPA filter (for quality) and a high CADR score (for power).

CADR vs. Other Jargon (ACH & CFM)

• CFM (Cubic Feet per Minute): This is just a raw measure of how much air the fan can move. It’s a “dumb” number. CADR is the “smart” number because it’s the CFM multiplied by the filter’s efficiency.
• ACH (Air Changes per Hour): This is the result you get. It tells you how many times per hour the purifier can clean the entire volume of air in your specific room. Health experts recommend 4-5 ACH for good air quality. The “2/3 Rule” for CADR is designed to help you achieve this 4-5 ACH target.

Your CADR Questions Answered (FAQ)

Final Verdict: How to Use CADR for a Smarter Purchase

Here is your simple, two-step plan to buy with confidence.

• Step 1 (Embrace): Use the Smoke CADR as your first and most important filter. Use the “2/3 Rule” to find the minimum power you need for your room size. And before you buy anything, look for the “AHAM Verifide®” seal to prove the claim is true.
• Step 2 (Extend): Once you have a list of models with the right CADR, look deeper. Ask the questions CADR can’t answer: Does it have a substantial Activated Carbon filter for VOCs and odors? What are its noise levels (dB) at the lower, quieter speeds?

By using CADR as your starting point, not your finish line, you can cut through the hype and find the perfect machine for your home.