CADR is reported in cubic feet per minute for smoke, dust, and pollen. To get air changes per hour: ACH = (CADR × 60) ÷ room volume. Rearranged, CADR = (ACH × volume) ÷ 60.
Many residential guides target about 4–5 ACH for a sick-room or wildfire setup; 2–3 ACH may be enough for everyday filtration. AHAM’s room-size map is often approximated as square feet ≈ CADR × 1.55, and the “two-thirds” rule says smoke CADR should be at least two-thirds of the room’s floor area in square feet.
Measure the room you will actually close the door on—open plans need more CADR.
Floor area first comes from the square foot calculator, then multiply by ceiling height for volume. If the same room feels hot, the AC ton calculator is the cooling counterpart.
How this calculation works
CADR_cfm = (ACH × L × W × H) / 60. Also reports AHAM-style room size and 2/3 floor-area check.