Measurement Guide

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Choosing the Correct Prehung Door Size and Handing

What Size is my Rough Opening?

Getting the rough opening size right the first time will save you a lot

of frustration when installing your doors. Framed rough opening sizes

are actually simple. Just add 2” to the width of the actual door size

and 2-1/4″ to the height of the actual door size

Why Does the Rough Opening Need to be Bigger than the

Door and Jamb? Three Reasons:

1. Room to adjust the door and the frame in the opening. Not all

rough openings are completely plumb and square. Leaving this extra

space allows you to perfectly plumb, level and square your door

installation.

2. Next, not all doors are the exact same size. The sizes of the door

will vary by manufacturer. Normally this isn’t much, but if your rough

opening was tight, or exactly the size of the door and the jamb, you

may not get the door to function properly without having room to

adjust.

3. Finally, this leaves room for expansion and contraction of the wall.

Yes, your wall gets bigger and smaller as the seasons change. It does

this by taking on moisture when it’s humid outside and shrinks when

temperature and humidity levels drop.

Again, we are talking about small amounts, sometimes less than

1/16″ of an inch, but this can be enough to make that once perfectly

fitting door start to stick, rub on the frame or not latch properly.

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Choosing the Correct Prehung Door Size and Handing What Size is my Rough Opening? Getting the rough opening size right the first time will save you a lot of frustration when installing your doors. Framed rough opening sizes are actually simple. Just add 2” to the width of the actual door size and 2-1/4″ to the height of the actual door size Why Does the Rough Opening Need to be Bigger than the Door and Jamb? Three Reasons: 1. Room to adjust the door and the frame in the opening.
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Rough Opening Tips •Verify the width and height of the door frame are each 1/2″ smaller than the rough opening width/height. •Verify the rough opening is square. The diagonal measurements should be the same. Maximum allowable deviation from square is normally 1/4″. •Verify the rough opening is level and plumb. The maximum allowable deviation is 1/8″ to 1/4″. What is my Door Handing? The easiest way to determine your door handing: Step into the open doorway with your back to the hinges.
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How to Measure Your Rough Opening 1. If you are measuring for a new construction, skip to Step 6. 2. If you are replacing an existing door, remove the casing or trim from one side of the door open. 3. Measure the width of the outside of the jamb in 3 places: top, center and bottom. Record the smallest of the measurements 4. Measure the height of the outside of the frame from the floor in 2 places: left and right. Record the smallest of the measurements 5.