Size Of The Room/Space It Can Cover
Generally speaking, most direct plug-in air purifiers cover rooms anywhere from 75 square feet to 200 square feet.
If you have a house that is 1,000 square feet, then it might be a good idea to get 5 to enjoy good, clean air.
Weight Of The Air Purifier
This is probably the least important thing since so many of them are very, very lightweight. On average, a standard direct plug-in air purifier will weight about half-a-pound to, at the most, two-pounds. Usually, the more it weighs, the bigger space it can purify.