How large of an area does the Purest Sleep Diffuser cover? January 23, 2019 17:53 The Purest will fill a 300 square foot room. (For reference, a 10x20 ft. room is 300 square feet.) Related articles What is the liquid capacity of the Purest Sleep Scent Diffuser? Is Yogabed™ easy to set up? Which sound machine is best for me? Which product is loudest?