CADR for your space
Each air purifier has a CADR number, which stands for Clean Air Delivery Rate. Most units will offer between 40 to 300 CADR. Multiply the CADR by 1.55 to calculate the optimal number of square feet that CADR can handle. For example, an air purifier with a CADR of 100 can effectively clean the air of a room that is 155 square feet. A unit with a lower CADR will also work in a room of that size, but not as efficiently or as effectively.