Air Purifier CADR Calculator (2026)

Q: What CADR do I need for my room size?

Room volume in cubic feet times air changes per hour, divided by 60. A 12 by 10 foot bedroom with 8 foot ceilings needs about 64 CADR for pets and 80 for allergies.

Q: How many air changes per hour should I aim for?

Allergies 4 to 5, pets about 4, general dust 2 to 3, smoke 5 or more. Add 1 change per hour when pets live in the home.

Q: Is a higher CADR always better?

Up to a point. Buy at or slightly above your minimum CADR — oversizing buys noise and cost, not cleaner air.

Q: Does CADR matter for pet hair and dander?

Yes — dander stays airborne for hours, so CADR is what clears it. A washable pre-filter catches hair and saves on replacements.

Q: What is the difference between CADR and the room size on the box?

Box room size is usually claimed at about 2 air changes per hour, too weak for allergies or pets. CADR is the tested, comparable number — always compare CADR.

The short answer: the CADR you need is your room volume in cubic feet, times the air changes per hour you need, divided by 60. A 12 by 10 foot bedroom with 8 foot ceilings needs about 64 CADR for pets and about 80 for allergies — most box claims promise far more than that. This free calculator does the exact math for your room, then shows you the purifiers that match it on Amazon.

CADR stands for Clean Air Delivery Rate: how many cubic feet of clean air a purifier delivers every minute. It is the one number that tells you whether a purifier can actually keep up with your room. Enter your room size, pick what you are fighting, and get the minimum CADR to shop for — no prices here, because prices move daily, so always check the live price before you buy.

What Size Air Purifier Does Your Room Need?

Measure your room, pick what you are fighting, and get the minimum CADR to shop for — plus the purifiers that match your number.

Measure in

Feet
Metres

Room length

Room width

Ceiling height (leave blank for standard 8 ft / 2.4 m)

What are you fighting?

Allergies (5 ACH)
Pets (4 ACH)
General dust (3 ACH)
Smoke (5 ACH)

ACH means air changes per hour — how many times the purifier filters your room’s full volume in one hour.

Pets in the home (adds 1 air change per hour)

Your minimum CADR

CADR is measured in cubic feet per minute (CFM). Always buy at or above your number — a purifier rated below it will never catch up, however long it runs. Prices move constantly, so check the live price before you buy.

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What CADR means, in plain language

CADR is Clean Air Delivery Rate: the volume of clean air, in cubic feet per minute, that a purifier delivers for a specific pollutant. Every purifier is tested three ways — smoke, dust, and pollen — and the honest number to shop by is the lowest of the three, because smoke particles are the smallest and hardest to catch.

ACH is air changes per hour: how many times the purifier filters your room's entire volume in one hour. Allergy guidance is 4 to 5 changes per hour, pets need about 4, general dust is fine at 2 to 3, and smoke or wildfire air needs 5 or more. This calculator uses 5 for allergies, 4 for pets, 3 for general dust, and 5 for smoke — and adds 1 change per hour when pets are in the home.

The room size printed on the box is the trap. Manufacturers usually claim it at about 2 air changes per hour, which is fine for a lightly dusty room and far too weak for allergies or pets. That is why a purifier "rated for 1,500 square feet" can still leave you sneezing: its CADR is too low for the air changes you actually need. Shop by CADR, not by the box claim.

The size bands this calculator uses:

Small room — CADR under 150: bedrooms and home offices up to about 200 square feet. Compact purifiers like the Levoit Core 200S class are enough here. For a quiet bedroom pick, see our DREO air purifier for the bedroom guide.
Medium room — CADR 150 to 300: living rooms and large bedrooms. This is where the Levoit Vital 200S-P and Winix 5500-2 class sit. If pets are the problem, start with our best air purifier for pets picks.
Large room — CADR over 300: open-plan living spaces. Winix 5510 and Coway Airmega Mighty class, or two smaller units placed at opposite ends.

Frequently asked questions

What is CADR on an air purifier?

CADR is Clean Air Delivery Rate: the cubic feet of clean air a purifier delivers every minute. It is tested separately for smoke, dust, and pollen — shop by the lowest of the three numbers, because smoke particles are the smallest and hardest to catch. A higher CADR means the purifier cleans a room faster, not that it filters better.

What CADR do I need for my room size?

Multiply your room volume in cubic feet by the air changes per hour you need, then divide by 60. A 12 by 10 foot bedroom with 8 foot ceilings is 960 cubic feet; at 4 air changes per hour for pets that is 64 CADR, and at 5 for allergies it is 80 CADR. This calculator does that exact math for your room.

How many air changes per hour should I aim for?

Allergies: 4 to 5 changes per hour. Pets: about 4. General dust: 2 to 3. Smoke or wildfire air: 5 or more. If pets live in the home, add 1 change per hour on top of your base number — pet dander is light, stays airborne, and needs more passes through the filter.

Is a higher CADR always better?

Up to a point. A purifier rated well above your number cleans faster, but it also costs more, uses more power, and runs louder on high. The right buy is a purifier rated at or slightly above your minimum CADR — oversizing by a lot buys noise, not cleaner air.

Does CADR matter for pet hair and dander?

Yes — dander is fine particles that stay in the air for hours, so CADR is exactly what clears it. Pet hair itself is caught by the pre-filter before it reaches the HEPA filter, so pick a purifier with a washable pre-filter if you have shedding pets; it saves real money on replacements.

What is the difference between CADR and the room size on the box?

The box room size is usually claimed at about 2 air changes per hour, which is too weak for allergies or pets. CADR is the tested, comparable number. Two purifiers can claim the same room size while one has double the CADR — always compare CADR, and use this calculator to find the number your room actually needs.

What CADR do I need for a 200 sq ft room?

Use the tool's formula: room volume x air changes per hour / 60. A 200 sq ft room with 8 ft ceilings is 1,600 cubic feet. At 4 air changes per hour for pets that is about 107 CADR; at 5 for allergies about 133 CADR. That sits in the tool's small-room band (under 150 CADR, up to about 200 sq ft) — enter your exact room size and what you are fighting in the calculator above for your number.

What CADR do I need for a large living room?

Use the tool's large-room band: CADR over 300, for open-plan living spaces. The tool's own worked example: a 25 x 20 ft space with 9 ft ceilings, for smoke at 5 air changes, needs 375 CADR minimum. A 20 x 15 ft living room with 8 ft ceilings, for allergies at 5 air changes, needs 200 CADR (medium band). Enter your room's length, width and ceiling height in the calculator — ceiling height matters, because taller rooms hold more air.

Real-world examples

These examples use the calculator's formula: room volume times air changes per hour, divided by 60. CADR figures are rounded up.

Small bedroom, 12 by 10 feet, 8 foot ceilings, pets (4 air changes): 960 cubic feet, 64 CADR minimum — small room band.
Living room, 20 by 15 feet, 8 foot ceilings, allergies (5 air changes): 2,400 cubic feet, 200 CADR minimum — medium room band.
Open-plan living space, 25 by 20 feet, 9 foot ceilings, smoke (5 air changes): 4,500 cubic feet, 375 CADR minimum — large room band.