The standard door height is 6 feet 8 inches. When framing a door opening, 2 5/8 inches must be added to the height of the door to leave room for the door jamb and flooring.
Standard door widths range from 12 to 48 inches. Framing out the width requires adding an extra 2 inches of space to accommodate the door jamb.
Doors are manufactured in standard sizes to reduce the manufacturing costs, which are generally passed on to the consumer in the final cost of the door. Custom-sized doors can be made to handle special situations, or standard-sized doors can be modified to fit an opening.