Guide to VELUX Window Sizes

Windows, Lanterns & Sun Tunnels
product guide
Guide to VELUX Window Sizes


How are Velux Windows Measured?

So, you know window size is important, but how are they measured? In the vast majority of cases, the size given represents the external frame, as opposed to the glazed area. This should roughly be the size of the hole you need to fill in your roof deck. However, this is not definitive, as the final size can vary when accessories such as a flashing kit or an insulation collar are taken into account.

All VELUX window sizes and codes are identified with a three-part series of letters and numbers. Once you know what each section of the code means, it will be much easier to find the best window for you. You will be able to check the window code on most websites (including our own).

We are also going to break down the different letters and numbers in each code right here, to help you get to grips with the coding system. Each part of this code references a different measurement, those being the type of window, the interior finish, the size, glazing and control mode.

What Does GGL, GGU, and GPU Mean?

The first part of the code is typically represented by a series of 3 letters – you’ll likely see an order such as GGL, GGU, or GPU, among others. Below, we have translated what each of these means:

G – the first G is always present. This is because it is a part of the code that confirms that this product is a window. 

G or P – The second G means that the window is a centre pivot. If there is a P instead of a second G, you are looking at a top-hung window.

L or U – L means that the frame of the window you are looking at is white painted pine, while the U means that it is made from white polyurethane, a sturdy and resilient plastic material.

What are VELUX Size Codes?

After these letters, you’ll be presented with a second code – the part that allows you to find out the size of the window. Below is a key – each letter in the VELUX window code translates to a width, while each number translates to a height. Be sure not to get these two-dimension keys mixed up.

There are various widths and heights available for VELUX windows, with some more common in buildings than others. Some of those common sizes are as follows:


  • CK = 550mm
  • FK = 660mm
  • MK = 780mm
  • PK = 942mm
  • SK = 1140mm
  • UK = 1340mm


  • 01 = 698mm
  • 02 = 778mm
  • 04 = 978mm
  • 06 = 1178mm
  • 08 = 1398mm
  • 10 = 1600mm

Note that pre-2014 windows will not have a 'K' in the code, though unless already installed, these will be rare.

What Are the VELUX Finish and Glazing Options?

Now we’ve reached the final section of the VELUX code – it is likely to be made up of different characters, with the first two referring to the internal and external finish respectively. The latter two characters tell you the pane variant and any other adds will be additional features. 

  • The Internal Finish - 0 (white polyurethane), 2 (white painted) or 3 (clear lacquer)
  • The External Finish - 0 (standard grey), 5 (black, only for conservation windows) or 8 (special colour)
  • The Pane Variant - 70 (double glazed), 66 (triple glazed), 67 (triple glazed), 68 (triple glazed), 69 (triple glazed), 62 (triple, extra noise reduction)
  • Add-ons:
  • 21U - electric.
  • 30R - solar.
  • 40 - the window has a smoke vent.
  • H – the window features a glazing bar
  • Q – the window boasts high-security features
  • R – the window has been designed to reduce the sound of rain

What are Flashing Codes?

If you are in the market for a matching VELUX flashing kit to go along with your new window is important to keep in mind their codes as well. Like the windows these are split into multiple parts, each referencing something unique.

EDW, EDP, EBW etc.

The first part of the code is very similar to the windows, telling us the flashing style and what type of roof material it is suitable for.

First Letter:

E – All VELUX flashing should have this. It simply tells us that the product is flashing.

Second Letter:

D – refers to single flashing

B – refers to twin flashing

K – refers to combi flashing

F – refers to sloping or vertical flashing

Third Letter:

Red Line vs Blue Line – Red lines mean the flashing is suitable for standard installation height, blue means recessed installation height.

Roofing Material




Plain Tile

Red Line




Blue Line




Flashing Width & Height

For ease, VELUX flashing codes us the exact same combination of letters and numbers to show their size. Please refer above to get the exact measurements in millimetres.

Additional Features

Also similar to the window codes, flashing codes are finished with a breakdown of the finer elements including the external finish and frame gap. There are quite a few combinations, so we recommend getting in touch if you have any specific questions. You can do so either by phone or using the chat box below.

Where Can I Find My VELUX Size Code?

To find the VELUX size code on your window is very straightforward – simply look for a plate in the top corner of the window frame. It is only noticeable when the window is open, so doesn’t affect the overall appearance of the window. It provides the code segments we explored above together in one sequence of letters and numbers.

This is a tried and tested method of telling customers all they need to know about a VELUX window. It will make it much easier for you to replace an existing window, but it can also be used to order spare parts should your window require them. It can even be used to help you buy replacement glazing or new blinds.

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