How to Guide

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Door size. Measure the width and height of your old door. Round these up to full inches
to find the size of the replacement door you’ll need. If, for example, your door measures
35-3/4 in. wide and 79-1/2 in. tall, you’ll order a 36 in. by 80 in. door. For double doors
this will be the total of both doors. For example, two 36 in. by 80 in. doors equal one 60
in. by 80 in. door size. Similarly, for a single door with sidelite(s), the width of the
sidelite(s) will need to be added to the door width.
Jamb (Frame) width. Measure from the
backside of the interior trim to the
backside of the exterior trim (Figure A).
Specify this jamb width when you order
your new prehung door. This guarantees
that the interior trim will fit flush to the
wall without adding “jamb extensions.”
Rough opening. You’ll have to remove the
interior trim to get accurate
measurements of the rough opening.
Measure the opening width between
framing members and from the bottom of
the sill to the top of the opening. Compare
these measurements to the rough opening requirements of your new door to make sure
it will fit.
How to accurately measure rough opening
· Measure the widths between the studs of the entryway 3 times; from the highest
points of the opening, the center points, and the lowest points. Record the
smallest width of the 3 measurements.
· Measure the height (from the bottom of the sill to the top of the opening) on both
sides and record the smallest measurement of the 2.
Rough opening recommendations
Getting the rough opening size right the first time will save you from frustration when
installing your doors. Framing and calculating rough opening sizes is quite simple.
Tip:
Not all rough openings are completely plumb and square. Leaving extra space allows
you to perfectly plumb, level and square your door installation.