Terminology for door ordering can be somewhat unfamiliar, but it's not a foreign language. Dealers and installers use reliable, common terms to indicate properly sized doors. But sizing is only one aspect of ordering a new door. Other details are also important.
Most Common Sizes
The majority of exterior doors are 36 inches wide and 80 inches tall, or 3 feet by 6 feet, 8 inches. The shorthand language for ordering it is 3-0-by-6-8, commonly pronounced by dealers and installers as, "three-oh-by-six-eight."
A Bit Smaller
Another commonly used door measures 32 inches wide, and 78 inches tall. The term used to order this door is 2-8-by-6-6.
Exterior doors are typically no shorter than 78 inches, but in some cases, when space is an issue, doors may be more narrow. It's not out of the question for a door to measure 30 inches wide, or 2-6.
The 2-Inch Rule
If your door is older or custom made, it may be different, but doors are typically measured in width by 2-inch increments.
Door swing direction is even more important than size. If the door swings in the wrong direction, it won't fit the jamb. This is the first thing to consider, and a simple procedure.
Determine the Swing Direction
Stand with your back to the exterior side of the door. The exterior side pushes away from your back, into the room.
Reach out to grasp the doorknob with one hand.
If your right hand is on the knob, it's a right-hand swing. If your left hand is on the knob, it's a left-hand swing.
Inswing or Outswing
The majority of exterior doors swing inward to the home. However, some doors swing out, particularly in Florida, or where high winds are common. The outswing door protects against wind better, because the door stop prevents it from moving inward. The procedure for identifying door swing direction is the same for inswing and outswing doors. Specify inswing or outswing when ordering.
Door Jambs and Walls
If you're going for a full replacement, door jambs should also come into play. Door jamb width should be the same thickness as the wall, plus about 1/8-inch to ensure it covers adequately.
The typical wall is built with two-by-four studs -- which actually measure 3 1/2 inches in width. Add 1/2 inch for drywall on the interior side, and 1/2 inch for siding on the exterior side, and the total is 4 1/2 inches. Add 1/8 inch for insurance, and the jamb should measure 4 5/8 inches wide.
If you're working with two-by-six walls, the standard two-by-six measures only 5 1/2 inches in width. Add 1/2-inch for drywall, 1/2 inch for siding, and 1/8 for insurance, for a total of 6 5/8-inch-wide jambs.
Use a common guideline to order new jambs with your door. It's standard practice to add 2 1/2 inches to the width of the door, and 3 1/2 inches to the height of the door for the jamb allowance. This provides a gap on the sides and top, to plumb and level the jamb inside the opening with shims.
The most widely used exterior door thickness is 1 3/4 inch. However, it's not uncommon for high-end or exclusive doors to have a thickness of 2 inches or more. Exterior doors are almost always solid.
Exterior doors have a 2- to 5-degree bevel on the side opposite the hinges. The purpose of the bevel is to facilitate opening and closing of the door without rubbing or scraping the jamb. If you're installing hardware on a new door, always look for the bevel. If it doesn't have a bevel, you can sand or cut it on the door with a hand planer.