Measuring Windows & Doors Accurately

How To Measure Windows & Doors - For The Technically Minded

To obtain a price on Comparemywindows.com, sizes do not have to be absolutely accurate.

Internal rough measurements are all that's required.

However, for the more technically minded, we have laid out how to accurately measure your windows - should you wish to do so.

General Rules:

·         Always measure from the outside.

·         Measure from brick to brick and not the existing door or window frame.

·         Measure in at least three different places and take off 10mm from both the final height and width to allow for a 5mm fitting allowance. This ensures the new frame fits squarely within the opening.

·         Include cills and any other add-ons in your measurements.

·         Use millimetres.

Measuring a Double Glazed Window

The height also needs to be measured between bricks at three points: Left, middle and right of the opening. The smallest of these measurements is taken as the height. Take off 10mm for fitting.

The width should be measured in between bricks at three points: Top, middle and bottom. The smallest of these measurements is taken as the width. Take off 10mm for fitting.

Measuring a Double Glazed Square Bay Window

This measurement guide applies to a three-sided square bay window with two corner posts. Calculations for corner posts are created by the Comparemywindows calculator.

Measure the height of each side window externally, brick to brick and include any existing window cill.

The width needs to be measured internally from frame edge to frame edge. Measure the width of each side window internally – they should both be the same.

Measuring an Entrance Door

Measure in at least three different places and take off 10mm from the final readings, but give both measurements so it’s clear which figures you’re providing.

The height should be measured between bricks at three points: Left, middle and right of the opening. Take off 10mm for fitting. The smallest of each width and height measurement is taken as the final figure.

The width should be measured between bricks at three points: Top, middle and bottom. Take off 10mm for fitting.

Make a note of whether the door opens inwards or outwards, and allow for the lay of the internal floor, so that the door is able to fully open inwards.

Measuring a Double Glazed Door with Side Panels or Top Light

Side Panels: The width should be measured at three points: Top, middle and bottom. This measurement should be taken from the centre point of the frame between the door and the side panel, to the outer edge of the side panel frame. Take off 10mm.

Top Light: The top light depth should be measured from the centre point of the frame between the door and the top light to the top of the door frame. This is called the transom drop for the top light.

Measure both side panels and top lights in addition to the measurement for the door itself. 

Did you mean one of these locations?
Compare Local Installers
  • See providers In your area.
  • See distance from your location.
  • Request quotes from any providers you choose to.
  • Compare companies side by side.
  • Send a summary of the work.
  • Providers will contact you to complete the quote.
Compare Prices Online
  • Get instant online quotes.
  • Input your detailed requirements.
  • See distance from your location.
  • Choose which providers you would like to contact you.
  • Compare companies side by side.
  • Send a detailed breakdown of the work.