How to Measure Rough Opening Size

The rough opening is the space where the door jamb will fit

  • Rough Opening Size and Door Size

    The rough opening should be 3/4″ wider and 1/2″ taller than the outside dimensions of the door jamb in order to easily fit the jamb into place.

  • For replacing an existing door

    It will be necessary to remove any interior trim around the door so you can see the house framing. Then you will need to find the studs that define the rough opening. Also, remove the threshold so that you can see the subfloor. If the threshold cannot be removed, you will need to establish the position of the subfloor with a probe.

  • Rough Opening - Width

    Measure the width between the studs at three places – at the top of the opening, at the middle, and the bottom. The smallest of these measurements should be recorded as the ‘rough opening’ width.

  • Rough Opening - Height

    Measure from the sub floor to the header beam above the door. For a straight topped door, measure on both sides and record the smallest measurement as the rough opening height. If you are replacing an arched door then also get the measurement in the center. In this case, the center measurement will be the rough opening height and the difference between the center and the outside corners height is the amount of “fall” on the arch. If you have any confusion or question about this please contact us.

Here is a schematic of a single door showing the relationship between Door Width, Jamb Width and Rough Opening Width:


For New Construction

The same rules apply for a new door as a replacement door. The rough opening must be ¾” wider and ½” taller than the outside dimensions of the door jamb. However, in many new constructions it may be possible to modify the building to fit the door unit to some extent. This will depend on other factors affecting the building design and also on how far along the building construction has proceeded. If you are in the design stage it is worth considering the whole design of your entryway and foyer in relation to the possibilities of door, sidelights and transom options. It is often noted by many real estate experts that the house entrance is one of the most important aspects that affect the appeal and the value of a home.

Threshold Height and Flooring

The Threshold is the sill at the bottom of the door that forms a barrier between the inside and outside. Unless specifically requested otherwise, all entry doors have an integral threshold. Eurolite doors for interior use have no threshold.

The nominal distance from the sub-floor the threshold top is 112“, however the maximum height of the flooring above the threshold should not exceed 114“, including all carpeting and rugs etc. If your flooring will be deeper than this then you will need to raise the threshold sufficiently. The rough opening height will be effectively reduced by the amount you raise the threshold. Please refer to the following diagram:


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