When selecting an air purifier, you will see a CADR Rating. CADR stands for Clean Air Delivery Rate, a metric developed by the Association of Home Appliance Manufacturers (AHAM) to measure an air purifier's effectiveness based on room size and the volume of clean air produced per minute.
Source: AHAM AC-1-2020 Method for Measuring Performance of Portable Household Electric Room Air Cleaners.
How to Calculate the CADR for Your Room
The U.S. Environmental Protection Agency (EPA) suggests that for effective cleaning, an air purifier should be able to cycle the air in a room multiple times per hour. To find the right fit, use the following standardized formulas:
1. The 2/3 Rule (EPA Recommended)
According to the "Two-Thirds Rule," the CADR of your air purifier should be at least two-thirds of the room's square footage.
Minimum Smoke CADR = Room Area (sq.ft.) x 2/3
Example: For a 120 sq.ft. room, you need a CADR of at least 80 CFM.
2. Conversion for International Standards
If your room is measured in square meters, the standard conversion factor used by industry experts is 0.12:
Applicable Area (sq.m.) = CADR (m³/h) x 0.12
Unit Conversions & Standards
To ensure a fair comparison between different brands, always check if the CADR is listed in CFM (Cubic Feet per Minute) or CMH (Cubic Meters per Hour).
Multiply CFM by 1.699
Divide CMH by 1.699
Technical References & Disclosures:
- CADR values are determined according to the ANSI/AHAM AC-1 test protocol, which measures the reduction of smoke, dust, and pollen in a controlled 1,008 cubic foot chamber.
- Room size recommendations are based on the assumption of 8-foot ceilings and a minimum of 4.8 air changes per hour (ACH), as recommended by the AHAM Verifide® program.
- EPA Disclaimer: The U.S. EPA does not certify air purifiers; however, they provide guidance on air cleaner performance through the Guide to Air Cleaners in the Home.
- Actual performance may vary depending on individual indoor environments, including ceiling height, layout, and existing pollutant levels.
