How do I measure a non-standard door?

Answered by Brett Kulina ~ October 9, 2013 ~ No Comments

I live in an old farmhouse and need to replace my non-standard front exterior door. How do I measure it? And is it best to order a customer door or to cut a standard door?


Brett Kulina

Troy, if you want to replace the front door of your old farmhouse, then you should first decide whether to replace the entire door frame assembly or just the door slab (which is the door only - meaning this replacement wouldn't include the hinges, the jamb, the threshold, etc.).

If you decide to replace just the door slab, then you'd need to remove the old door from its hinges and install a new door that has the exact same measurements and knob location. Keep in mind that the new door would need to be the same width, height, and thickness in order to fit securely into the existing door frame and close properly. The standard height of most new doors is 80 inches, although 7-foot and even 8-foot doors are also readily available. The most common exterior door width is 36-inches.

However, if your old door is an odd size, then your best bet may be to replace the entire door frame assembly with a new pre-hung exterior door. A pre-hung door would include a door slab, a door frame, a threshold, and all of the weatherstripping that helps keep out water and drafts when the door is closed. You can purchase a new pre-hung exterior door for as little as a few hundred dollars, and most units are fairly simple to install with a few basic tools and some general DIY carpentry skills.

Before you purchase a pre-hung exterior door, you will need to measure the existing door opening. To do this, expose the entire door frame by removing the interior trim around the door, then measure the space. When ordering your new door, you will need to know the width and height of the existing door opening, as well as the thickness of the exterior wall. If your door opening is an odd size, as you indicate yours may be, then it may be best to purchase a pre-hung door that is smaller than the existing opening. If the framing (i.e. door opening) is 35", then it would be easier to purchase a 34" prehung door and fill in the 1" void around the door frame, as opposed to trying to enlarge the opening to accommodate a standard 36" prehung door.

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