Determining the Correct Size When Buying a Pre-hung Exterior Door

Because pre-hung exterior doors arrive from the manufacturer already mounted in their frames, they tend to fit more tightly against the weather and require less labor during installation. These units are sized to match the rough opening of a doorway, so accurate measurement of that opening is necessary before making a purchase.

Door

Door

A pre-hung exterior door is a popular option for a homeowner replacing an entry door, since the manufacturer ships it already seated inside a frame. This reduces the time and effort required of whoever installs it, and it also helps the door resist weather more effectively. The way these doors are sold is based on the size of the doorway's rough opening, so anyone hoping to buy a correctly sized pre-hung door needs to measure that rough opening with care.

Step 1

Use a pry bar to take off the molding around the door's opening. The rough opening is the gap into which the door itself will eventually go. Molding, which some people call trim, is the wood or other material sitting directly around the opening and holding the door in position. It has to come off because it conceals the actual dimensions of the rough opening.

Step 2

Check that the door studs sit level. These studs are the beams behind the door molding that form the frame of the rough opening. Should the studs be out of plumb by more than 1/4 of an inch, they must be realigned more accurately before a reliable rough opening measurement can be taken.