Measuring to the millimetre is important, which is why it should be entrusted to experienced installers.

While measuring the width, height and depth of the window is enough for internal blinds measurement, it gets more complex for external blinds. Moreover, every inaccuracy can be serious. See what the window opening measurement for external blinds entails and why you shouldn’t do it on your own.

For external blinds, it is also necessary to account for the distance of the blinds from the window in addition to the height and width of the window opening. The preparation and measurement of the protective box and places on the path through which control elements lead are also important.

 The measurement then varies depending on whether you want to install the external blinds:

  • onto the frame of the window, 
  • onto the façade
  • or underneath the façade..

When performing the measurements for the blinds, the installation method is key. 

  1. Sub-plaster installation (i.e. underneath the façade) is measured in two phases. The first measurement is performed once the window frames have been mounted but the house has not yet been fitted with its insulation layer. The measurement is done for sub-plaster boxes and cases or sandwich plates for the slat guiding rails. The second measurement is done for the opening for the blinds themselves on the finished façade.
  2. Visible installation (i.e. onto the window frame) involves measurement of the window opening for the blinds and the space for the protective box. In addition to the width and height of the opening and the distance of the blinds from the window, sufficient space on the window frame and the method of controlling the blinds are also important.
  3. Mounting onto façades requires measuring the position for the anchoring points, the width of the box and the opening for the blinds, as well as the distance of the blinds from the window, on which the method of anchoring depends.
„When mounting the blinds underneath the façade, the communication and coordination with the tradesmen can be more difficult as the mounting of the blinds is linked to the insulation layer, window mounting and electricity distribution systems. However, a skilled installer will look after all the technical details and sort everything out for you.“

Lukáš Musil

Sales Manager

When measuring for the installation of exterior blinds, the installer must also know:

  • whether the wall surface is perfectly even,
  • the distance of the axis of the blinds from the frame of the window,
  • where and how the blinds are to be anchored,
  • paths of cables,
  • the position of the passage (and therefore the gearbox),
  • whether the customer wants insect screens,
  • and whether anything obstructs the movement of the blinds .
During each construction, it is good to keep in mind whether the project already involves any blinds, so that the blinds fit correctly and the building is prepared for their installation. This is the rule for larger jobs such as the “Tabulový vrch” villa park in Olomouc.

A width difference as small as 3mm can have serious consequences.

The width and height of the construction opening for external blinds is measured at three points (at the top, bottom and in the middle), which makes the finished blinds fit exactly. The maximum tolerance is ±2 mm. In case of a greater deviation, the blinds may not work properly, and in addition the wall surface will seem uneven to the naked eye.

“Whether the blind has been poorly measured or the wall surface is narrowing or widening, a difference of more than a few millimetres tends to be a big problem. In such cases, the blinds no longer function properly or look good, so we suggest getting the installers to choose another installation type or suggest wall surface modifications. If the inaccuracy is minor, we can make the blinds based on an average or the narrowest measured dimension. However, the customer needs to keep in mind that the unevenness will be visible to the naked eye,” explains Lukáš Musil from NEVA, further emphasizing the importance of accurate measurements. 

„If a roller blind has been improperly measured, it can simply be shortened in the shop, but you can’t really modify the dimensions of an exterior blind. Any adjustment of the dimensions is resolved by making new slats for the blind. Each place therefore needs to be measured very meticulously.“

Lukáš Musil

Sales Manager

The measurement is also influenced by the control method.

The control method has a major influence on the measurement, which is why it is important to determine it right at the beginning. The control method depends on the type of motor, the type of electrical installation and the type of accessories.

In case of handle-controlled blinds, the position of the gearbox in relation to the window and its passage into the interior must be measured so that the interior handle can be installed to begin with. The installer knows during the inspection whether everything will fit into the window area and, if it is not possible to do the handle passage through into the interior, they will propose another (e.g. motor) control method.

If you have chosen blinds driven by electric motors, it is necessary to take the electrical installation into account. Cables are typically led from the interior through a drilled hole and connected to the control switch or smart home system. so it is important to make sure that the cables are long enough.

What are the most frequent errors when measuring blinds?

A lot of errors can be made when measuring the window opening for outdoor blinds. “If the end customer contacts us with self-made measurements or sends us data from the construction documentation, we can hook them up with our partner installation company, who will in turn measure the blinds and recommend suitable guiding rails, whose dimensions and selection are crucial for proper operation of the blinds,” explains Lukáš Musil.

The installers are familiar with the precise measurement procedures for blinds and their experience allows them to foresee any potential complications.

If there is already an error in the measurement, it usually concerns

  • neglecting the gap (at least 2 cm) between the sill and the bottom profile of the blinds,
  • underestimating an under- or over-sized window, which cannot be fitted with blinds
  • or anchoring into a non-supporting element (insulation layer, lintel).

Measurement of external blinds depends on every detail – just a minor error and the blinds may not work properly or even be possible to install at all, so you shouldn’t do external shading measurements by yourself. Hire an expert installation company which is qualified to carry out both the measurement and installation of blinds.  

For example, you can choose from our partners, who are trained directly by us at NEVA.


Jan Gajdoš

Jan Gajdoš works as a product manager. He studied building construction at the Secondary Technical School in Prostějov and still uses the knowledge acquired in this field. He has worked in NEVA since 2006 and is responsible for introduction of manufacturing technologies and development of the existing range of products.

All articles by the author