How to Measure an Opening for a New Entrance

Measuring an opening for new framing and doors is simple in theory, but it is all too easy to make small and avoidable mistakes that can lead to big headaches later.

There are two basic approaches to sizing new entrances: measuring the opening and letting Special-Lite determine net frame (and door) sizes, or providing Special-Lite with net frame sizes. If providing net frame sizes to Special-Lite, it is important to provide tip-to-tip frame dimensions, because our doors and frames are not manufactured to be field adjustable. We will not make the frame undersize to allow for shim space, so the accuracy of the sizes you provide is critical. For retrofit installations, it is important to adhere to the following recommended best practices when measuring openings.

To Measure for New Doors and Frames:

Inspect the entire opening, both interior and exterior, noting differences in:

  • Floor heights and conditions (rough or finished)
  • Opening width dimensions and wall conditions
  • Header or ceiling heights and conditions
Measuring Width Measuring Height

It may be necessary to remove a piece of trim to determine the exact nature of the rough opening. This will ensure you take correct measurements from masonry to masonry. Getting accurate measurements of the rough opening at this stage should avoid any nasty surprises when removing the old entrance.

Measuring the Opening (Figure A):

  • Measure interior-side opening width (horizontal) at top, center and bottom.
  • Measure exterior-side opening width(horizontal) at top, center and bottom.
  • Record the smallest of these six rough opening width dimensions.
Figure A Measuring Opening

(Figure B)

  • Measure opening height (vertical) from underside of header to floor at left and right jamb and center locations. Be sure to allow for final floor height if floor is still in rough condition. Account for any header height differences, interior to exterior.
  • Record the smallest of these six dimensions as the rough opening height.

Figure B Measuring Opening

Completing Special-Lite Estimate/Order Forms:

  • Use a consistent format for recording dimensional units (decimals vs. fractions).
  • Record rough opening sizes, remembering it is better to err on the small side.
  • Be sure to note whether dimensions provided are rough opening or net frame size.
  • Use separate forms for each opening.

The Special-Lite Estimate/Order Forms make a great checklist to ensure that all required information has been provided. They also eliminate guesswork and help to reduce order lead times.

One Last Tip:

Finally, always carefully inspect and measure new entrance products to ensure everything is sized correctly before demolition of the old entrance. Following these guidelines should greatly reduce the likelihood of problems and frustrations at installation.