Air Purifier Calculators
Free tools to help you size and shop for an air purifier based on real math, not guesswork.
CADR Calculator
Figure out the minimum CADR (Clean Air Delivery Rate) rating you need based on your room dimensions and how aggressively you want the air cleaned.
IndoorBreathing.com · Air Purifier Sizing Tool
CADR Calculator
Enter your room dimensions and how aggressively you want the air cleaned. We'll tell you the minimum CADR rating to look for — and which real, currently-available purifiers clear that bar.
Your Room
ft long
ft wide
ft
Air changes per hour (ACH) is how many times the purifier fully cycles the room's air in an hour. 4 ACH is the standard recommendation for allergy relief; hospitals use 6–8.
Minimum CADR you need
225CADR
Achievable with a mid-range purifier
Floor area
144 sq ft
Room volume
1,152 cu ft
Air changes/hr
4
Real purifiers that clear this CADR
Formula:
Required CADR = (Length × Width × Ceiling Height × ACH) ÷ 60 — the same method AHAM-certified purifiers are rated against. Room volume in cubic feet, divided into the hourly rate, tells you how much clean air the unit must deliver per minute.