CADR stands for clean air delivery rate. This varies with each brand and make of air purifier. What this depends on how good a filter the purifier has and how much air it can push through this filter. Manufacturers provide CADR for their products for different particle ranges. Use the rating given for smoke or dust. If the value is given CFM (cubic feets per minute), you can convert it to CMH by multiplying it by 1.7 (approx).