Using a tape measure, determine the width of the door from stud to stud. The measurement reflects the rough opening of the existing door. The door width is measured at the top, the center, and along the bottom of the door opening. Start at the side jambs at the widest accessible portion.Click to see full answer. Consequently, how big should a door rough opening be?The height of common doors is 6 feet 8 inches. The standard height of the rough opening for a door is the door height plus 2 5/8 inches. The additional room allows for a 3/4-inch top jamb, a shim space above the door jamb and the thickness of underlayment and finish flooring.Furthermore, how big is the rough opening for a 30 inch door? So, if you have a bedroom door that is 30″ wide (which is considered a 2/6 or 2′-6″ door) just add 2″ to the width and frame it 32″ wide. The height is 80″ (which is considered 6/8 or 6′-8″) add 2-1/2″ to the actual door height and frame it 82-1/2″ high. what is the standard size of a patio door? The size of your wall area and how much natural light you want to let in will help you determine the best size for your sliding glass door. Standard patio doors are 6 feet, 8 inches tall. Width size varies depending on whether the patio door is a two- or three-panel configuration.How big should the opening be for a 36 inch door?The doors are also a standard 80 inches tall. Presuming the door is a 36-inch wide door, the dimensions of your opening should be 37½ inch wide by 81½ inch tall.