CADR Ratings Explained: How to Size an Air Purifier for Your Room

CADR—Clean Air Delivery Rate—is the most important number to understand when buying an air purifier. Without it, you're flying blind. With it, you can match any purifier to any room with confidence.

What CADR Actually Means

CADR measures how much clean air (in cubic feet per minute) a purifier delivers for three specific particle sizes: smoke (0.1–1 μm), dust (0.5–3 μm), and pollen (5–11 μm). A purifier with a smoke CADR of 200 delivers 200 cubic feet of smoke-particle-free air per minute.

CADR is tested and certified by AHAM (Association of Home Appliance Manufacturers) in standardized conditions. Unlike manufacturer claims for "room coverage," CADR is a third-party, apples-to-apples comparison metric.

The Sizing Formula

The standard formula: Room area (sq ft) × ceiling height ÷ 60 = minimum CADR (CFM) for 1 air change per hour (ACH). For adequate air quality, you want 4–5 ACH.

Simpler rule of thumb: CADR should equal at least ⅔ of room square footage. A 300 sq ft room needs at least 200 CADR. For landfill neighbors, we recommend sizing up—aim for CADR equal to room square footage for 4+ ACH.

CADR Comparison Table

One Purifier or Multiple?

One large purifier in an open-plan space is generally more efficient than multiple small units. But closed rooms—bedrooms especially—need their own unit. An open-plan living/dining/kitchen of 500 sq ft plus a 200 sq ft bedroom means two purifiers: one mid-range unit for the main area and one bedroom unit.

Don't try to filter a closed bedroom from a hallway purifier. Air in closed rooms doesn't circulate to where the purifier sits.

Placement Matters

Put the purifier where it can draw in the most polluted air—typically on the floor, away from walls, with clear space around all intake vents. The "dirty" air flows in at the bottom; clean air exits at the top. Running it in the room's corners or against walls reduces effective CADR by restricting airflow.