everything. Order too small and the room feels dark. Order too large and you are left with costly alterations. Understanding VELUX window sizes before you buy saves time, money, and a whole lot of hassle on site.
This guide breaks down every VELUX size code, what the measurements actually mean, and how to choose the right window for your project.
What Do VELUX Size Codes Actually Mean?
VELUX uses a two-part code system for all of its roof windows. The first part is a letter that tells you the width. The second part is a number that tells you the height.
For example, in the code MK04, the "M" stands for the width category, and "K" refines it further. The "04" refers to the height. Once you understand this, navigating any VELUX size guide becomes straightforward.
Here is a quick breakdown of how the system works:
- First letters = width of the window
- Numbers = height of the window
- Larger numbers = taller windows
VELUX Window Sizes: Full Code & Dimension Reference
This is the section most developers and builders need most. Below is a clear comparison of the most common VELUX window sizes and their actual dimensions.
|
VELUX Code |
Width (mm) |
Height (mm) |
Best Use |
|
CK02 |
550 |
780 |
Small loft rooms, tight roof pitches |
|
CK04 |
550 |
980 |
Compact bathrooms, en-suites |
|
MK04 |
780 |
980 |
Standard loft bedrooms, studies |
|
MK06 |
780 |
1180 |
Living areas, open-plan lofts |
|
MK08 |
780 |
1400 |
Larger bedrooms, good light output |
|
PK08 |
940 |
1400 |
Spacious rooms, rear extensions |
|
SK06 |
1140 |
1180 |
Wide roof spans, premium installs |
|
SK08 |
1140 |
1400 |
Large loft conversions, studios |
|
UK08 |
1340 |
1400 |
Maximum light, commercial use |
|
UK10 |
1340 |
1600 |
High-end residential, large roofs |
These are the rough opening sizes. Always check the installation manual for the exact structural opening required, as this will be slightly larger.
What Is VELUX MK04 and Is It Right for Your Project?
The VELUX MK04 is one of the most popular sizes in the UK market. It measures 780mm wide by 980mm tall. It sits right in the middle of the range, not too small to feel cramped and not so large it dominates the roof.
It works well for:
- Standard loft bedroom conversions
- Home office spaces
- Smaller living areas where you need decent daylight without major structural work
The MK04 is a solid choice for most domestic projects. If your room is larger or you want a real flood of natural light, stepping up to an MK06 or MK08 is worth considering.
How to Use a VELUX Size Guide for Your Roof
Choosing the right size is not just about the room below. Your roof pitch, rafter spacing, and tile type all affect which VELUX window sizes will work.
Here is a simple process to follow:
- Measure your rafter spacing. VELUX windows need to fit between rafters without cutting structural timbers where possible.
- Check your roof pitch. Most VELUX windows work between 15° and 90°. Some models have a minimum pitch requirement.
- Think about the room size. As a rough rule, your glazed area should be around 10-15% of the floor area for good natural light.
- Match the code to your opening. Use the table above to find the closest size. Remember, you need the structural opening to be slightly larger than the window itself.
If you are also looking at flat roof options, our flat glass rooflights are worth a look alongside pitched roof windows.
Centre-Pivot vs Top-Hung: Does Size Change?
Yes, the operating style affects how the size feels in practice. A centre-pivot window rotates around the middle. A top-hung window opens outward from the top.
For low ceilings or tight loft spaces, top-hung models often feel less intrusive when open. However, both styles are available across the same size range. The VELUX MK04, for example, is available in both configurations.
Glazing Options and How They Affect Your Choice
Larger VELUX window sizes bring in more light, but they also lose more heat if the glazing is poor. For UK building regulations compliance, you will typically need double or triple glazing.
At Skylights Roof Lanterns, our roof windows collection includes triple-glazed options that meet current energy efficiency standards. If you are working on a new build or major renovation, triple glazing is almost always the right call.
When to Choose a Rooflight Instead
Not every project needs a pitched roof window. If you have a flat or low-pitch extension, a rooflight or roof lantern will do a far better job of bringing light into the space below.
Our range covers flat roof applications, while our roof lanterns work brilliantly over kitchen extensions and garden rooms. Both are available in bespoke sizes, unlike standard VELUX codes which are fixed.
Common Mistakes When Ordering VELUX Windows
A few things trip people up every time:
- Confusing the rough opening with the window size. Always add the required frame allowance.
- Not checking the roof pitch minimum. Some models won't seal properly below a certain angle.
- Ordering for the room, not the rafter spacing. The rafter gap limits what you can fit without structural work.
- Assuming all codes are the same across product ranges. VELUX uses the same code system, but flashings and accessories vary by roof type.
Conclusion:
Understanding VELUX window sizes before ordering can save a huge amount of time, cost, and installation stress later on. From compact CK models to large-format UK sizes, choosing the right dimensions comes down to your roof structure, room size, and the amount of natural light you want to bring into the space.
Whether you are planning a loft conversion, upgrading an existing roof window, or comparing options for a new project, taking the time to match the correct VELUX code to your space will always lead to a better end result.
If you need help choosing the right solution for your roof, explore the full range of roof windows and glazing options from Skylights Roof Lanterns or get in touch with the team for expert guidance on sizing, glazing, and installation suitability.
