Air Purifier Size Calculator
Air purifiers get sold based on marketing hype, not on what your room actually needs. You see “powerful cleaning” or “removes 99.97% of particles,” but nobody tells you the real question: is this machine strong enough for YOUR room?
I studied air quality and how it moves through spaces. What I learned is that one number matters above all others: CADR, which stands for Clean Air Delivery Rate. It’s not exciting, but it’s accurate.
This calculator gives you that number. Not a guess, not a sales pitch. Just the science of what your room needs.
Calculate Your CADR
How This Works
The calculator uses two pieces of information to find your answer:
Your room size. Bigger rooms need bigger air cleaning power.
Your goal. Are you just removing everyday dust, or are you dealing with allergies, pets, smoke, or pollution? Each goal requires a different level of cleaning power.
The calculator then uses the AHAM standard for CADR testing and ASHRAE ventilation guidelines to tell you exactly how much air-cleaning power your purifier needs to deliver every hour.
The number you get is measured in cubic metres per hour (m³/h) or CFM (cubic feet per minute). That’s the CADR you should look for when shopping.
What Your Result Means
The calculator gives you two numbers:
Minimum CADR. Look for a purifier at or above this number. It’s the floor. Anything below this won’t clean your room efficiently for your goal.
Ideal CADR. This is the sweet spot. A purifier here will clean your air faster and handle real-world conditions like not being in the perfect center of the room.
Let’s say your room needs 160 m³/hour minimum CADR. That means you should look for purifiers rated at 160 or higher. A purifier rated at 200 m³/hour would be even better. It will clean faster and work better when placed off to the side.
Important Limitations
This is an estimation tool, not a guarantee. Real-world performance depends on many things:
Your room layout and furniture. If the purifier is crammed in a corner, it won’t work as well as if it sits in open space.
Filter condition. A clogged filter doesn’t deliver its rated CADR. Change filters on schedule.
Where the purifier sits. The further it is from pollution sources, the less effective it becomes.
Air leaks. If your room has huge gaps around the door or window, clean air escapes and dirty air leaks back in.
Typical accuracy. This calculator is usually within plus or minus 15-20% of real performance, depending on your room conditions.
What this calculator does NOT measure:
✗ Removal of gases or odours (requires activated carbon)
✗ Removal of chemical fumes (VOCs)
✗ Performance with the door open or windows open
✗ Health outcomes (it shows air cleaning, not medical results)
This calculator tells you what air-cleaning power you need. Whether that translates to health improvements depends on your specific situation.
Scientific Basis
This calculator uses:
AHAM Standard A.350.1. This is the official standard for how air purifier CADR is tested. Manufacturers use this standard to rate their machines. It ensures that when two purifiers both claim 160 m³/hour CADR, they’re measured the same way.
Learn more about AHAM standards →
ASHRAE 62.1. This is the standard for ventilation and indoor air quality. It defines how many air changes per hour (ACH) are recommended for different spaces and different pollution levels.
Learn more about ASHRAE 62.1 →
EPA Indoor Air Quality Guidelines. The US Environmental Protection Agency provides guidance on effective ventilation rates for homes.
Read EPA guidance →
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