VELUX Window Sizes Made Easy - Velux Size Guide - VELUX Sizes

Posted by Skye Tunks on 1st February 2020

Why not make shopping for your new windows even easier? 

In this blog, we are going to go through our exclusive VELUX Window Sizes Guide, because as we all know, it can be confusing with the different range of sizes, model numbers and window codes that are applied to each one. Let’s discover your exact window match now, it will only take a few minutes.

Firstly, you must know the exact measurements available and with our size guide, you can see below the exact sizes from which you can choose from.

The good thing about VELUX sizes is the consistency that comes hand to hand with them. Over the majority of the VELUX operation they have not altered most the VELUX sizes of the roof window. 

Click our interactive VELUX size chart below to view all products in below VELUX window sizes.

 55cm 66cm 78cm 94cm 114cm 134cm
 70cm CK01 SK01 
 78cm CK02
 98cm CK04 FK04 MK04  PK04  UK04
 118cm CK06  FK06 MK06  PK06 SK06 
 140cm  FK08 MK08  PK08  SK08  UK08
 160cm MK10  PK10  SK10  UK10
 180cm MK12 

If you are looking to replace an existing VELUX ggl sizes, then you can easily use the size guide above to see which new generation code relates to your old roof window code (compare with the diagram below) to determine your VELUX window sizes.

To explain, if your current VELUX branded window has a code of GGL2, then your new VELUX windows would now have the code MK08. For an even further explanation, take another review of the diagram above and compare your old code, to the new. The one shown in this example is a VELUX ggl 4 -> VELUX SK06.


A Guide to your VELUX Window Codes and Sizes.

It's a known fact that VELUX is always improving their products, to help ensure that they maintain the high quality that they are known for. These continuous improvements over the years have resulted in some of the older styles becoming out of date in terms of shelf life.

However, this is not a problem, as the new off-shelf VELUX flashings can be made to fit any older window, in many circumstances. However, The VELUX ggl 5, now VELUX FK04 standard VELUX window size has now changed. Which means replacement flashings are not available for this model.

Here are the old VELUX window size chart, serial number, and number codes -

  • VELUX Window sizes 55 (W) x 78 (H) code 102 or C02 or CK02

  • VELUX Window sizes 55 (W) x 98 (H) code 104 or 6 or C04 or CK04

  • VELUX Window sizes 78 (W) x 98 (H) code 304 or 1 or M04 or MK04

  • VELUX Window sizes 66 (W) x 118 (H) code 206 or 5 or F06 or FK06

  • VELUX Window sizes 78 (W) x 118 (H) code 306 or 14 or M06 or MK06

  • VELUX Window sizes 78 (W) x 140 (H) code 308 or GGL2 or M08 or MK08

  • VELUX Window sizes 134 (W) x 98 (H) code 804 or 7 or U04 or UK04

  • VELUX Window sizes 114 (W) x 118 (H) code 606 or 4 or S06 or SK06

  • VELUX Window sizes 94 (W) x 160 (H) code 410 or 3 or P10 or PK10

  • VELUX Window sizes 134 (W) x 140 (H) code 808 or 8 or U08 or UK08

For example. A VELUX GGL4 will be replaced by VELUX code SK06. VELUX replacement flashings can be used to replace the roof window to minimise internal plasterboard alterations.

Above, is the list of window sizes and code varieties that they may have on them, but this all depends on when the window was purchased.

But do remember that window sizes are for the external window frame and not internal measures.

These are strictly VELUX pitched roof window sizes. Not VELUX flat roof window sizes.

Where Are Velux Brand Window Codes Located?

You can easily find VELUX window codes on the top right-hand edge of the roof window when you open it. The data plate tells you the type of window it is, and the window size shown through the code (as seen below.)

As shown in the above example, 304 would be 78cm x 98cm and the bottom window code 4, would be 114cm x 118cm.Finding your VELUX structural opening size is critical to the install of your roof window. Here is a breakdown on your structural opening size for your VELUX roof window. 

Replacing your roof window. 

When shopping our store for VELUX roof windows. If you’re replacing your roof window it is important to remember that you can change cosmetic features such as the operation (21U, 30), internal finish (GGL, GGU) and glazing (70,68,66......). However, you cannot change the VELUX window size. The VELUX window size code determines your new replacement roof window. For example, if you are replacing a GGL -4, you could change to white painted, triple glazed top hung. However, we recommend sticking to the replacement size. GGL -4 + SK06. So, your replacement would be a GGL SK06 2068. 

VELUX structural opening size and how to find your VELUX structural opening size.

To determine the structural opening size for a VELUX roof window, you will need to measure the rough opening in the roof structure. Here are the steps you can follow:

  1. Access the roof structure: To measure the rough opening, you will need to access the roof structure. This may require a ladder or scaffolding, depending on the height of the roof.
  2. Measure the width: Measure the width of the rough opening at its widest point. Take two measurements, one at the top of the opening and one at the bottom, and use the smaller of the two.
  3. Measure the height: Measure the height of the rough opening at its tallest point. Take two measurements, one at the left side of the opening and one at the right side and use the smaller of the two.
  4. Measure the slope: Measure the slope of the roof, also known as the pitch, in degrees. This measurement is important for selecting the correct flashing for your roof window.
  5. Record the measurements: Record the measurements of the rough opening and the slope of the roof and use this information to select the appropriate VELUX roof window and flashing for your installation.

It's important to be accurate in your measurements to ensure that you select the correct size roof window and flashing, as well as to ensure a proper fit and watertight seal. If you are unsure about your measurements or the suitability of a particular roof window and flashing, it's recommended to consult with a professional roofer or a VELUX representative.

(RED) Standard VELUX flashings. Your VELUX structural opening sizes should be the VELUX window should go as the following. 

VELUX Structural opening size = VELUX sizes - external frame dimension (H) + 45mm overall top to bottom. VELUX window external frame size (W) + 20-30mm at each size of the window (Left & Right)

(BLUE) Standard VELUX flashings. Your VELUX structural opening sizes should be the VELUX window should go as the following. 

VELUX Structural opening size = VELUX sizes - external frame dimension (H) + 145mm overall top to bottom. VELUX window external frame size (W) + 25-30mm at each size of the window (Left & Right)

Finding the structural opening size for your Velux window is easy! Begin by measuring the outer frame of your window. The size of the VELUX structural opening will be slightly smaller than the window frame size. Next, use a tape measure to measure the height and width of the window opening. Be sure to measure from the exterior wall surface to the interior wall surface. You should now have the dimensions of your structural opening size!

VELUX structural opening sizes can differ in many ways due to factors such as plasterboard, insulation and installation accessories. However structural opening sizes for VELUX windows can give us a blank canvas to help you find the perfect roof window for your home.

If you have found your structural opening sizes for your VELUX window. You can watch our below video on how to make the VELUX sizes opening Here.

Can't find your VELUX code?

Can't find your VELUX size code? Do not panic. Let us do the hard work! We recommend measuring the visible VELUX glass size on your roof window. VELUX sizes are in the format (W)cm x (H)cm and take an image of the roof window. You can then forward these details into Although the VELUX glass size does not give us the exact external frame measurement. It gives us a rough guide. No matter if you have the smallest VELUX window or the biggest VELUX window, our sales team will try our hardest to find your perfect, new, stylish roof window!

Why choose VELUX?

VELUX is the leading roof manufacturer in the world. Dating all the way back to 1942, their manufacturing and product design is desirable by everyone. VELUX have a huge range of roof window sizes for both pitched roof windows and flat roof windows. VELUX define the market with high quality affordable roof windows to double your daylight in your home. No matter the VELUX window sizes, we can always find the best option for you.

Not looking for VELUX today?

Our brand portfolio is one of biggest and most diverse in the roof window industry. From huge stock lists from brands of every price point. YARD Direct have you covered. Why not try our window butler to help you find your perfect roof window size today.

If you would like any further information with anything related to roof window repairs, fitting a new flashing set to an old roof and VELUX windows, or how to replace an old VELUX flashing, then please feel free to visit here to find out more, or visit our Window Butler where you will be guided to the perfect window for your project.