CADR Rating Explained

CADR stands for Clean Air Delivery Rate. It is the volume of filtered air an air purifier delivers each minute, measured in cubic feet per minute (CFM) and tested separately against three particle sizes: smoke, dust and pollen.

One thing to settle before anything else, because it trips up almost everyone: CADR is what the machine produces, not what your room requires. A purifier rated "Pollen 292" delivers 292 cubic feet of pollen-free air a minute. It is not a statement that your room needs 292. Your room has its own number, worked out below, and the job is to find a machine whose rating clears it.

If you are here to size a purifier, the answer is one line: multiply your room's square footage by 2/3. A 300 sq ft bedroom needs a CADR of at least 200. Everything below explains why that rule is what it is, what the number does and does not prove, and how to check any manufacturer's claim yourself.

I chair the AHAM Air Cleaners Council, the industry group that oversees the AC-1 test standard this rating comes from. That means I have an obvious interest in you taking CADR seriously, so I have tried to be equally clear about where it falls short.

What does CADR stand for, and how is it calculated?

CADR is the Clean Air Delivery Rate, the full form of the acronym. It was developed by AHAM, the Association of Home Appliance Manufacturers, as a way to compare air purifiers on a single number that accounts for both how much air a machine moves and how much of the particle load it actually captures.

The standards were developed at a different time, some decades ago when air quality and air cleaners were less popular. Behind the scenes, air filtration testing standards are being reviewed, as awareness of the importance of indoor air quality has grown since COVID. The need to measure air cleaning in larger room sizes is one example.

The calculation behind it is simple:

CADR = airflow (CFM) × filter efficiency

A purifier moving 200 CFM through a filter capturing 100% of a particle size has a CADR of 200 for that particle. Move 200 CFM through a filter capturing 75%, and the CADR is 150. This is why CADR is harder to game than either number alone. A very efficient filter with poor airflow scores badly, and so does a powerful fan behind thin media.

The laboratory does not calculate it that way, though. CADR is measured directly. The purifier runs at maximum fan speed in a sealed test chamber while an independent lab tracks how fast the particle concentration falls against natural decay. The result is expressed in CFM of clean air delivered.

Three particle ranges are tested, and each gets its own number. Since 2024 there is also a PM2.5 CADR, roughly an average of the smoke and dust figures.

What CADR rating do I need for my room?

Multiply your room's square footage by 2/3. That number is the minimum CADR you need to clean the air 4.8 times per hour, the rate AHAM uses to calculate the suggested room size printed on the AHAM Verifide seal, and the rate allergists recommend when the goal is controlling an airborne allergen rather than general freshening.

Another way to picture 4.8 air changes per hour: the purifier filters all the air in the rated space every 12.5 minutes.

A few examples:

• 150 sq ft (small bedroom) → CADR ≥ 100
• 300 sq ft (primary bedroom) → CADR ≥ 200
• 500 sq ft (large living room) → CADR ≥ 335
• 800 sq ft (great room) → CADR ≥ 535
• 1,200 sq ft (open-plan main floor) → CADR ≥ 800

Working backwards from a purifier you are already looking at, the same rule inverts: CADR × 1.55 = the room size it covers at 4.8 air changes per hour.

This is not an Oransi rule. AHAM uses it to calculate the suggested room size on the Verifide seal, ENERGY STAR uses the same two-thirds ratio in its room air cleaner criteria, and the EPA's Guide to Air Cleaners in the Home publishes a sizing table that works out to 0.65 CFM per square foot — the same ratio, arrived at independently. Worth knowing that the EPA table gives the number without naming the air change rate behind it, which is why its figures look slightly lower than ours at every room size.

CADR by room size — quick reference

For 9-foot ceilings, multiply the CADR requirement by 1.13. For 10-foot ceilings, multiply by 1.25. To convert CADR between units: 1 CFM = 1.699 m³/h.

When to go above the minimum

The 2/3 rule is a floor for ordinary conditions, and AHAM says as much. Three situations justify going higher, and it is worth knowing what each buys you.

For wildfire smoke specifically, size so the smoke CADR equals your room's square footage rather than two-thirds of it. Smoke particles are the smallest of the three test sizes, and during a smoke event the outdoor air is a continuous source pushing particles back in through the building envelope. At 1.0× you are running roughly 7 air changes an hour, which is what it takes to hold a room below outdoor levels rather than merely tracking them.

There is a ceiling on this in practice. Every step up the ladder costs airflow, which costs noise and watts, and a machine you turn off because it is too loud delivers nothing. Go higher than 4.8 when you have a reason, not by default.

Oransi CADR ratings by model

Every Oransi HEPA model is AHAM Verifide. We publish smoke CADR across the line because it is the most demanding of the three ratings. A purifier that hits its smoke CADR target will comfortably handle dust and pollen in the same room.

The AirMend™ series is designed, engineered and assembled in Radford, Virginia. Noise figures and full lab results are published on each product page, and every certification we hold is listed on our air purifier testing page.

Here is the AHAM Verifide listing for the Mod and Mod Jr., taken from AHAM's own directory:

What is a good CADR rating?

"Good" depends entirely on your room. A CADR of 100 is excellent for a 150 sq ft nursery and inadequate for a 400 sq ft living room. The right way to judge a CADR rating is against your specific room size, using the 2/3 rule above.

That said, AHAM treats any rating above 240 as "high" and uses that threshold in some of its certifications. The published scale tops out at 450 — AHAM does not publish higher figures, so a purifier listed at 450 tested at or above that ceiling. For most homes, 200 to 350 is the useful range. Below 100, a purifier is suited only to small enclosed spaces.

How common ratings map to rooms:

• CADR 50–100: small offices, closets, bathrooms
• CADR 100–200: bedrooms, home offices, dorm rooms
• CADR 200–300: living rooms, primary bedrooms, classrooms
• CADR 300–450: large living areas, open floor plans, small apartments
• CADR 450+: whole-floor coverage, large open spaces, commercial settings

One caution on the top end. A high CADR is only useful at a fan speed you will actually run. A machine rated 400 that is unbearable on high is, in practice, a 200 CADR machine, because that is the speed it will live on.

Why CADR has three numbers: smoke, dust and pollen

AHAM tests purifiers against three particle types, each standing in for a size range. All three appear on the AHAM Verifide seal.

• Smoke CADR: particles 0.09 to 1.0 microns. The smallest of the three and the hardest to capture. If a purifier hits its smoke CADR target for your room, it will comfortably handle dust and pollen too.
• Dust CADR: particles 0.5 to 3.0 microns. Includes household dust, dust mite debris, and the carrier particles for many indoor allergens.
• Pollen CADR: particles 5.0 to 11.0 microns. Tree and grass pollen, ragweed, and mold spores. Use this figure if pollen or mold is your issue.

A well-designed HEPA purifier will have similar numbers across all three, usually within 10 to 20 of each other. A large gap, where smoke is much lower than dust, points to adequate filtration paired with weak airflow at the speeds fine-particle removal requires.

When in doubt, size on the smoke CADR. It is the most conservative of the three, and it is the one we publish across our line for exactly that reason. It also makes our numbers look smaller than they would if we quoted pollen, which is the point.

CADR vs CFM vs ACH

Three related numbers, regularly confused, and the differences matter for sizing.

CFM (cubic feet per minute) is the total volume of air the purifier moves through itself, regardless of what comes out the other side. A purifier's CFM is always higher than its CADR, sometimes much higher, because CADR is the clean air delivery rate after the filter's actual capture efficiency is applied. Two machines with identical CFM can have very different CADR.

ACH (air changes per hour) is how many times a purifier can replace all the air in a particular room in an hour. It depends on both CADR and room volume, which is why the same machine has a different ACH in every room. For allergy and asthma control the target is 4.8 ACH, which is what the 2/3 sizing rule produces.

The short version: CFM is what the unit moves. CADR is what it actually cleans. ACH is whether that is enough for your room.

For a fuller treatment of air changes and how they relate to room volume, see our guide to air changes per hour, and for sizing by square footage, air purifier room size.

CADR at the speed you actually run it

Here is the problem nobody in this category addresses properly, and it matters most in the room where people most often put a purifier.

CADR is measured at maximum fan speed. The bedroom is the one place you will not run maximum fan speed.

The gap is large. Manufacturers who will discuss it put sleep mode at roughly a third to a quarter of the rated figure. A machine rated 400 delivers something like 100 to 130 overnight. Size your bedroom with the rated number and then run the unit on sleep, and you are getting perhaps a quarter of the air changes you calculated — often closer to 1 ACH than 4.8.

That is not a reason to distrust CADR. It is a reason to size against the speed you will live with. Four practical ways through it:

• Skip "sleep mode" and use fan speed 1 or 2 instead. Sleep mode is usually a step below the lowest numbered speed and disproportionately slower. The first numbered speed is often close to silent, and delivers meaningfully more.
• Pre-clean, then step down. Run high for an hour before bed with the door closed, then drop to a quiet speed to hold the level. Clearing a room is a bigger job than keeping it clear, and this puts the noisy part of the work where you are not asleep for it.
• Size up so the quiet speed is enough. If you need 200 CADR at night, a machine rated 250 will not deliver it on low. One rated 400 might. Oversizing is how you buy quiet, and it is the main reason to choose a larger machine for a small bedroom.
• Ask for the decibel figure at the speed that delivers the rated CADR, not the quietest setting on the box. The two are rarely the same number and only one of them describes the machine doing its job.

This is where fan and motor design shows up. A purifier that moves more air per watt needs less fan to hit the same CADR, which means the speed you can sleep through sits closer to the speed that was rated. It is the reason we design around airflow per watt rather than peak airflow, and the reason the AirMend line delivers full room coverage from a unit that sits on a table.

One disclosure gap worth naming, since I chair the council that sets this standard: almost nobody publishes CADR at each fan speed. It is expensive to run the formal lab testing at each fan speed and all of the standards are based on the highest speed. Buyers ask for it constantly and there is no requirement to provide it. Until that changes, ask the manufacturer directly, and as a proxy ask for the CFM if a formal CADR is not available.

What your actual room does to the number

CADR is measured in a sealed 1,008 cubic foot chamber with the air deliberately mixed. Your bedroom is not that chamber, and four things in a real room pull the delivered performance below the rated figure.

• Open doors. A purifier sized for a 300 sq ft bedroom is sized for a closed 300 sq ft bedroom. Leave the door open to a hallway and the effective volume it is fighting is much larger. Either close the door or size for the combined space.
• Placement against furniture. Intake and outlet both need clear air. A unit wedged behind a sofa or under a nightstand short-circuits, pulling in the clean air it just produced. A foot of clearance on the intake side is the practical minimum.
• Ceiling height. The 2/3 rule assumes 8 feet. Vaulted and 10-foot ceilings are common in exactly the great rooms people try to cover with one machine, and they add 25% to the volume.
• Continuous particle sources. CADR describes how fast a purifier clears a one-time particle load. A cat, a gas stove, or an open window near a road is a source that keeps refilling the room. Against a continuous source the purifier reaches an equilibrium rather than clearing the air, and more CADR raises where that equilibrium sits.

None of this makes CADR less useful. It is the reason to size up rather than to the minimum, and it is why we recommend sizing on smoke CADR against a room you have actually measured.

It is also worth knowing that CADR adds. Two purifiers in the same room deliver the sum of their ratings, so a 500 sq ft living room needing 335 can be served by two 200-CADR units as readily as one 350. For anything above roughly 700 sq ft, multiple units are usually the better answer anyway. In not only on cost, but because CADR assumes well-mixed air and one machine at one end of a long room will clean the air near itself far better than the air at the far wall.

How to check any air purifier's CADR yourself

A CADR printed on a box is a manufacturer's claim. A CADR in the AHAM Verifide directory has been measured by an independent laboratory, and AHAM randomly selects certified products and retests them. Those are different things, and the second one is checkable in about thirty seconds.

1. Go to the AHAM Verifide directory at ahamverifide.org.
2. Search the brand and model exactly as it appears on the unit.
3. Read the three CADR figures and the suggested room size, which AHAM calculates at 4.8 air changes per hour.

If a purifier is not in that directory, its CADR has not been independently verified. That is not automatically a mark against it, participation is voluntary but it does mean the number came from the manufacturer. Search any brand, including ours.

What the AHAM suggested room size actually means is worth stating precisely, because it is more specific than most people assume. It is the room size at which the air cleaner reduces smoke particle concentration by 80% to a new steady state, accounting for room sources and for air infiltrating from outside and from connected rooms. It is a steady-state figure for a working room, not a best case for a sealed one.

Three things to watch while you compare:

Not every published CADR is an AHAM CADR. This is the trap that catches careful shoppers. A brand publishes figures tested to the Korean standard (SPS-KACA 002-132), and some brands publish a single composite CADR from the Chinese GB/T 18801 standard rather than three separate particle numbers. Those are real tests. They are not the AHAM AC-1 result, and a number from one standard cannot be lined up against a number from another. If you see one composite CADR instead of separate smoke, dust and pollen figures, you are not looking at an AHAM rating.

Units. Some brands market CADR in cubic metres per hour. One CFM is 1.699 m³/h, so a 235 CFM machine can be advertised as 400 and look like a far bigger number than it is. CFM is the US standard.

The air change rate behind a room size. A coverage claim means nothing unless you know the air change rate it assumes, and most brands do not state it. We publish coverage at 4.8 ACH because that is the AHAM basis.

Here is the arithmetic that exposes it. A brand advertising "covers 1,800 sq ft" is almost always quoting one air change per hour. The machine will process 1,800 sq ft worth of air once in an hour. At the 4.8 changes that allergy control needs, the same machine covers around 375 sq ft. As a rough translation, divide any advertised coverage figure by about 4.8 to get its real coverage at the AHAM rate. Do that before comparing two machines and the field looks very different. Why this is not yet regulated, and what may change, is on our air purifier testing page.

Is CADR trustworthy? A straight answer

Search CADR and you will find videos and articles arguing the rating is meaningless. Since I chair the council that oversees the standard, here is the honest version.

The criticisms that are fair:

• CADR is measured at maximum fan speed. If high is too loud to live with, you will never see the rated number.
• CADR is measured with a new filter. It describes day one. A thin filter with little media can test well and fall off within months, and nothing in the rating captures that.
• CADR covers particles only. It says nothing about odors, VOCs or gases, which need activated carbon and a different test entirely.
• The smallest particle in the method is about 0.09 microns. Ultrafines below that are not measured, though HEPA media does capture them.

The criticism that is not fair: that CADR can be gamed. It is the hardest number in this category to inflate, because it is measured by an independent laboratory, in a repeatable way, published in a public directory, and subject to random retesting. Compare that to a percentage-removal claim, where the brand chooses the chamber, the particle, the duration and the reporting.

I see the alternative regularly. A salesperson holds a particle counter next to a purifier and the reading drops. It is compelling, and the test is not fake. But it measures one spot in one room over one minute, ignores airflow across the whole space, and says nothing about noise or how the filter behaves in month six. That demonstration is what you get when CADR is dismissed.

So: CADR is a floor, not a ceiling. It is the only certified, independently verified, publicly searchable performance number in residential air cleaning, and it should be the first thing you check. It should not be the last.

What to check after CADR

Once a purifier clears the CADR bar for your room, four questions remain and none of them are answered by that number:

• Noise at the speed you need. Check the decibel figure at the speed required to deliver the rated CADR, not the quietest setting advertised.
• Filter media. Ask how much media is in the filter and how deep the bed is. A large filter holds its performance far longer than a thin one. Be cautious when a manufacturer will not say.
• Odors and gases. A separate mechanism and a separate standard. If cooking smells, pet odor or off-gassing are part of why you want a purifier, you need carbon — see the TrueCarbon series.
• Ozone and safety. Look for mechanical filtration certified by CARB. No ionizer, no ozone generator, no UV.

CADR per dollar, done honestly

A fair question people ask and almost nobody answers well: which purifier gives the most clean air per dollar? The trap is comparing sticker prices, because a cheap machine with an expensive filter on a short replacement cycle is not cheap.

The comparison worth making is CADR divided by (purchase price + one year of replacement filters), with the noise figure noted alongside. Three numbers, one line of arithmetic, and it reorders most shortlists. A $150 unit needing $60 of filters every six months costs $270 in year one. A $200 unit with a $50 twelve-month filter costs $250 and may well deliver more air.

Our own figures, so you can run it: the AirMend™ 150HB is $179.84 with a $49.84 HEPA filter rated for 12 to 18 months. TrueCarbon filters are $89.84 on a twelve-month cycle. These are the list prices and do not include any discounts. Put those against whatever you are comparing us to, including the filter line, and the ranking will differ from the one you get on price alone.

Two honest caveats on this metric. It rewards loud machines, because airflow is cheap and quiet airflow is not, so carry the decibel figure through the comparison or you will talk yourself into something you switch off. And it says nothing about whether the unit survives year three, which is a motor question and the most expensive thing to get wrong.

The standards behind each of those, which bodies run them, where they stop, and what our products score against them are all set out on our air purifier testing page. Independent editorial testing is collected on our air purifier reviews page.

Summary

CADR is the best starting point for comparing air purifiers, and on its own it is not enough to choose one.

What I would check, in order:

• CADR, sized to your room with the 2/3 rule, using the smoke figure
• That the CADR is listed in the AHAM Verifide directory rather than only on the box
• Noise at the speed required to deliver that CADR
• Filter media: how much, how deep, and how long it lasts
• Motor quality — the most expensive and most failure-prone component in the machine
• Safety: CARB-certified mechanical filtration, no ozone

CADR is administered by AHAM, the Association of Home Appliance Manufacturers. Oransi is a member, and this article was written by Peter Mann, founder of Oransi and Chair of the AHAM Air Cleaners Council — the group that oversees AHAM's air cleaning test standards, including the AC-1 particle CADR.