EngineerHub.orgDrawing No. EH–HH–001 // Household Engineering Tools
Air Purifier CADR Calculator
Reviewed August 2026
Turn room size into a practical CADR target, compare it with EPA sizing guidance, and see how many purifiers are needed.
01 // Room & target
02 // Required CADR
Background & method
The EPA's Guide to Air Cleaners in the Home publishes a room-area to minimum-CADR sizing table (CADR ≈ 0.65 × room area in ft², based on an 8 ft ceiling), which is consistent with AHAM's ~4.8 air-changes-per-hour sizing basis for AHAM Verifide-certified units. The direct relationship CADR = room volume × ACH is used for the user-selected target. For other ceiling heights, this page scales the EPA 8-ft table in proportion to room volume as a transparent engineering extrapolation, not as an additional EPA or AHAM rule.
FAQ
Clean Air Delivery Rate is the volume of contaminant-free air delivered by the purifier. Higher CADR means faster particle removal.
Room-size charts often assume an 8 ft ceiling. A taller room contains more air, so the same CADR produces fewer clean-air changes per hour.
No. CADR is a particle-removal performance metric. Gas removal depends on activated carbon or other sorbent media and is not represented by the particle CADR.