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How to Measure Windows

Anyone planning renovations in the house needs to measure the correct dimensions of doors and windows first. This is the only way to ensure a smooth installation procedure for new windows and to avoid complications. We created a manual that simplifies this measuring process and describes the necessary steps to determine the right measurements. The dimension determined in such a way may then be used to order your window via our product configurator.


  • pen and paper
  • blueprints


  • one tape measure

1. Preparation

Old houses usually already have doors and windows (wood, uPVC or aluminium) installed. In order to determine their dimensions, you will need to take the existing measurements from the installed components. It can be very helpful to work with an existing blueprint, because the relevant data is already mentioned there. However, due to regular renovation processes, the measurements of old buildings may differ from the original blueprint. Please re-measure and do not rely entirely on the blueprint (Fig. 1).

If you measure and write down the exact sizes of doors and windows, you may use them at a later date for additional accessories such as shutters and insect protectors, without having to re-measure. Before you can start measuring, you will need a tape measure, pen, paper. You should then write down all dimensions for the respective windows from the blueprint and copy them with the date of change.

Regardless of whether you are dealing with an old or new building, measuring always has to be done from the inside and outside. Possible deviations determine whether to install the window from the inside or the outside.

2. How to measure windows in old buildings

To get correct numbers, you should draw a brief sketch of the window on a piece of paper and later on fill in the dimensions you measure. This sketch should also include the position of the window handle and the spatial requirements of opening and closing the window.

The dimensions of windows and doors are always measured from the point of view of a person looking out from the inside!

  • Follow the next step to measure the width, determining first the window’s upper, followed by its lower section width. The smaller number should be employed as the initial value. As there needs to be a gap for seals, you should deduct 20 mm from the dimensions measured.
  • Now measure the height at two points and use the smaller value again as a basis. Deduct 10 mm. In old buildings, the windowsill might well be higher on one side. Accordingly, you should to add the connecting profile’s height to your calculation. This is necessary, since the profile size is always added to window measurements.

Usually, the connecting profiles for windows are standardised to 30, 40 or 50 mm. If the measurement is not clear you should always use the smaller value to make sure the new one really fits in the given wall opening.

Example: You measure a height of 132.0 cm. Deduct 10 mm and the resulting size is now 131.0 cm. The width shows the measurements 124.0 cm in the upper part and 123.0 cm in the lower part. Deduct from the smaller value here as well – 123.0 cm minus 20 mm. The final resulting width of your window is 121.0 cm.

If you need help with taking the right measurements for windows in old buildings, you can find a detailed video manual here.

3. How to measure windows in new buildings

It is much easier to measure the correct dimensions for windows in new buildings. The reason for this is that the windows are not yet installed and that only the respective height and width of the wall opening has to be measured.

  • In the first step you will simply need to measure the height of the wall opening – left-hand and right-hand – and take the smaller value as the basis. You determine the relevant measurement by deducting 20 millimetres from the smaller value.
  • The width can be taken in the same way. Measure the width from the upper and the lower parts in order to mark possible differences. The smaller value serves as the basis. Deduct 20 mm for the final measurement. Doing so, you can ensure that there will be enough space.

Example: The measured dimensions of the wall opening are 1,260 (width) and 1,460 mm (height). After deducting 20 mm from each value you will be left with a size of 1,240 (width) and 1.440 mm (height).

Should problems or questions occur while measuring windows, you can find a video manual on this topic here.

Taking correct measurements is essential for determining the dimensions of new windows and guaranteeing smooth installation. Using this manual and watching the video material will make this a very simple process. Furthermore, you will have learned the basics for measuring doors as well. Determining the measurements for front and balcony doors is identical in almost every way.

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