How to Measure for an Entry Door
To determine the size for a new entry door, measure the existing door unit:
- Measure the width and height of the existing door.
- Measure the width of the door jamb between the interior and exterior door casings to determine the thickness of the wall. Door jambs are the sides of the door frame that are perpendicular to the door and cover the wall studs. On a standard 3½” stud wall, the door jamb usually measures 4 5/8” wide to allow for 1/2″ drywall on the inside and 1/2″ plywood sheathing on the outside.
- Measure the outside dimensions of the door casings around the door frame. Door casings are the top and side pieces of the door frame on the inside and outside that attach to the wall studs and door jambs to hold the door in place. Most exterior doors have 2” wide by 1¼” thick brick mold for the exterior casing around the door, and 2¼” to 3¼” wide by 11/16” thick molded trim casing on the interior.
- Take the measurements to your building supply or home center and match the size of the door, thickness of the jamb, and exterior dimensions of the casing to the existing door on your house. The interior dimensions of the casing are not as crucial, since the casing overlaps onto the wall.