Measuring 8 1/2" diameter and 2 3/4" H Ventilator Cutout Diameter 4 3/4" , screw hole to Screw hole diameter 7.75" Installation on flat surface This water resistant 4" solar powered ventilation comes with intake & exhaust blades. It moves up to 900 cu.ft./hr of air when powered on solar and with a slight breeze provides passive ventilation at night.