Air Purifier Size Calculator
Enter the room area and why you are buying - dust, allergies, or smoke. The calculator gives the CADR number to look for on the certification seal, and the marketing square-footage claim to ignore.
CADR is the only spec that survives contact with physics: the marketing room-size numbers assume one lazy air change an hour, while allergies want four or five - which is why the allergy version of this calculator doubles the machine. The room that matters most is the bedroom, because eight hours of breathing is the longest exposure anyone gets.
How to use
- Measure the room the purifier will live in, door closed.
- Pick the honest reason - allergies and smoke run bigger machines.
- Buy the certified seal, not the square-footage headline.
Frequently asked questions
What size air purifier do I need for my room?
Look for a CADR around two-thirds of your square footage for general air, doubled for allergies, more for smoke. A 300-square-foot bedroom wants roughly CADR 300 for allergy season - the calculator prices your room and reason.
What does CADR mean on air purifiers?
Clean Air Delivery Rate - the certified cubic-feet-per-minute of filtered air, tested on dust, pollen and smoke. It is the only number verified by an independent standard; everything else on the box is marketing geometry.
Why does the marketing claim a bigger room than the CADR suggests?
Room-size claims assume one air change per hour; allergy guidance wants four or five. Same machine, different math - the calculator runs the honest version for your reason.
Where should I run an air purifier?
The bedroom first - eight hours of breathing is the longest exposure of the day - with the door closed so the sizing holds. Run it low at night for noise, high when you return home, and replace filters on schedule.