How to do a correct garage door measurement:
Garage door sizes are always shown and listed as the width first and then the height.
Width: Measure the width of the opening at the widest point.This is the distance between the right and the left side of the finished opening.
Height: Measure the height of the opening at the highest point.This is the distance between the floor and the top of the finished opening.
Side Room: Measure the width of the areas beside the openings. At least 4″ is required on each side for installation of the vertical track.
Headroom: Measure the area between the top of the door opening to the ceiling.Garage doors require 12″ of headroom for the door installation and additional 3″ for an opener. (For installation with less than 12″, special hardware required)
Depth: Measure the distance from the opening to the rear of the garage.The door height plus an additional 18″ is required for the garage door installation or an additional 4’2″ plus door height if installing an automatic garage door opener.