Velux and Roof Window Sizes
VELUX makes 27 roof window sizes, from CK01 (55 x 70 cm) to UK10 (134 x 160 cm). Each code is a letter for the width and a number for the height, so MK06 is 78 x 118 cm and PK08 is 94 x 140 cm. The sizes are the outer frame. Below, every size is drawn to scale on VELUX's own grid, checked against its size guide in October 2026.
| Height | C55 cm | F66 cm | M78 cm | P94 cm | S114 cm | U134 cm |
|---|---|---|---|---|---|---|
| 0170 cm | CK01 | · | · | · | SK01 | · |
| 0278 cm | CK02 | · | · | · | · | · |
| 0498 cm | CK04 | FK04 | MK04 | PK04 | · | UK04 |
| 06118 cm | CK06 | FK06 | MK06 | PK06 | SK06 | UK06 |
| 08140 cm | · | FK08 | MK08 | PK08 | SK08 | UK08 |
| 10160 cm | · | · | MK10 | PK10 | SK10 | UK10 |
| 12180 cm | · | · | MK12 | · | · | · |
Drawn to the same scale. Blue sizes have a top-hung version VELUX marks as suitable for emergency escape; bold codes are the ten in VELUX's guide. Not shown: BK04 (47 x 98 cm), MK27 (78 x 62 cm) and PK25 (94 x 55 cm).
What size is my Velux window?
Every VELUX window made since 1968 has a type plate in the top corner of the sash, behind the ventilation flap. It shows the window type (such as GGL for a centre-pivot window or GPU for top-hung) and the size code. Type it in to see the size and its equivalents.
Open the window and find the metal plate on the top of the sash. Type the code, such as MK06, or an older code like M06 or 306.
Every Velux roof window size
| Code | Size (cm) | Frame (mm) | Older codes |
|---|---|---|---|
| BK04 | 47 x 98 | 472 x 978 | B04 |
| CK01 | 55 x 70 | 550 x 698 | C01, 101, 9 |
| CK02 | 55 x 78 | 550 x 778 | C02, 102 |
| CK04 | 55 x 98 | 550 x 978 | C04, 104, 6 |
| CK06 | 55 x 118 | 550 x 1178 | C06 |
| FK04 | 66 x 98 | 660 x 978 | F04, 204 |
| FK06 | 66 x 118 | 660 x 1178 | F06, 206 |
| FK08 | 66 x 140 | 660 x 1398 | F08 |
| MK27 | 78 x 62 | 780 x 624 | M27 |
| MK04 | 78 x 98 | 780 x 978 | M04, 304, 1 |
| MK06 | 78 x 118 | 780 x 1178 | M06, 306, 14 |
| MK08 | 78 x 140 | 780 x 1398 | M08, 308, 2 |
| MK10 | 78 x 160 | 780 x 1600 | M10, 310, 13 |
| MK12 | 78 x 180 | 780 x 1800 | M12, 312 |
| PK25 | 94 x 55 | 942 x 550 | P25, 425 |
| PK04 | 94 x 98 | 942 x 978 | P04, 404, 31 |
| PK06 | 94 x 118 | 942 x 1178 | P06, 406 |
| PK08 | 94 x 140 | 942 x 1398 | P08, 408 |
| PK10 | 94 x 160 | 942 x 1600 | P10, 410, 3 |
| SK01 | 114 x 70 | 1140 x 698 | S01, 601 |
| SK06 | 114 x 118 | 1140 x 1178 | S06, 606, 4 |
| SK08 | 114 x 140 | 1140 x 1398 | S08, 608, 10 |
| SK10 | 114 x 160 | 1140 x 1600 | S10, 610 |
| UK04 | 134 x 98 | 1340 x 978 | U04, 804, 7 |
| UK06 | 134 x 118 | 1340 x 1178 | None |
| UK08 | 134 x 140 | 1340 x 1398 | U08, 808, 8 |
| UK10 | 134 x 160 | 1340 x 1600 | U10, 810 |
Width x height of the outer frame, from VELUX's UK size guide (April 2026). Not every size comes in every type of window. The K in today's codes marks windows made since 2014; codes like M06 are from 2001 to 2013 and numbers like 306 are older still. VELUX's conservation windows have their own codes, such as CC04 (55 x 98 cm) and MC08 (78 x 140 cm).
FAKRO and Keylite sizes
FAKRO and Keylite make windows in the same nominal sizes as the common VELUX ones, but the codes work differently. FAKRO's size 06 is 78 x 118 cm, whereas a VELUX code ending 06 only tells you the height. The real frames also differ by a few millimetres, so compare the actual sizes before swapping one make for another.
| Size (cm) | VELUX | FAKRO | Keylite |
|---|---|---|---|
| 55 x 78 | CK02 | 01 | 01 |
| 55 x 98 | CK04 | 02 | 02 |
| 55 x 118 | CK06 | 16 | 01C |
| 66 x 98 | FK04 | 03 | None |
| 66 x 118 | FK06 | 04 | 03 |
| 78 x 98 | MK04 | 05 | 04 |
| 78 x 118 | MK06 | 06 | 05 |
| 78 x 140 | MK08 | 07 | 06 |
| 78 x 160 | MK10 | 13 | None |
| 94 x 118 | PK06 | 08 | None |
| 94 x 140 | PK08 | 09 | 07F |
| 94 x 160 | PK10 | 80 | 07 |
| 114 x 118 | SK06 | 10 | 08 |
| 114 x 140 | SK08 | 11 | None |
| 134 x 98 | UK04 | 12 | 09 |
From FAKRO's August 2026 catalogue and Keylite's 2025 price list. Keylite also makes 134 x 140 cm (code 10, like VELUX UK08).
Escape roof windows for loft conversions
A loft bedroom may need a window big enough to climb out of in a fire. Approved Document B asks for an opening of at least 0.33 m², at least 450 mm high and 450 mm wide, with the bottom of the opening no more than 1100 mm above the floor. The window has to stay open on its own.
VELUX marks its manual top-hung windows as suitable for emergency escape in 10 sizes: CK06, FK06, MK04, MK06, MK08, PK06, PK08, PK10, SK06 and UK04. Centre-pivot windows aren't marked. VELUX doesn't mark its 55 x 98 cm size (CK04) either, and FAKRO and Keylite say theirs isn't suitable for escape. Ask your building control officer about the sill height for a roof window, as the guidance treats roof windows in loft conversions separately.
Velux roof balcony sizes
The VELUX roof balcony (once sold as Cabrio) is a top-hung window over a lower section that opens out into a small balcony. It comes in MK19 (78 cm wide), PK19 (94 cm wide), SK19 (114 cm wide), all 252 cm tall, for roofs pitched at 35° to 53°.
Replacing a roof window
VELUX has kept the same standard sizes while its codes changed, so a new window fits the hole an old one came out of. In England, a new roof window needs a U-value of 1.4 or better, or a Window Energy Rating of band B. For prices, see our Velux loft conversion cost guide.
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Frequently asked questions
What is the standard Velux window size?+
There isn't one standard size, but some come up again and again. VELUX's own guide picks out ten: FK06, MK04, MK06, MK08, PK06, PK08, SK06, SK08, UK04 and UK08. MK04 is 78 x 98 cm and MK06 is 78 x 118 cm, both common in lofts.
What does a Velux code like CK04 mean?+
On VELUX's size chart, the letter sets the width and the number sets the height. C is 55 cm wide and 04 is 98 cm tall, so CK04 is 55 x 98 cm. The K shows it's a current-generation window, made since 2014.
What is the biggest Velux window?+
Of the standard roof windows, UK10 is the biggest at 134 x 160 cm. The VELUX roof balcony, which opens out into a small balcony, is 252 cm tall in all. The smallest roof window is CK01 at 55 x 70 cm.
What size Velux window do I need for a fire escape?+
An escape window needs an opening of at least 0.33 m², at least 450 mm high and wide, with the bottom of the opening no more than 1100 mm above the floor (Approved Document B). VELUX marks its manual top-hung windows as suitable for emergency escape in 10 sizes, from CK06 up. CK04 isn't one of them.
How do I find out what size my Velux window is?+
Open the window and look for the metal type plate on the top of the sash, behind the ventilation flap. It shows the window type and size code, such as GGL MK06. Older windows show older codes, like M06 or 306, which map to today's sizes.
Are Fakro and Velux sizes the same?+
The common sizes match in centimetres, but not to the millimetre, and the codes mean different things. FAKRO's size 06 is 78 x 118 cm, the same nominal size as a VELUX MK06, but in a VELUX code 06 just means the height. Always compare the actual frame sizes before replacing one with the other.
Is MK04 the same as M04 and 304?+
Yes. VELUX's replacement table maps MK04 (since 2014) to M04 (2001 to 2013), 304 (1992 to 2000) and 1 (before 1992). It's the same 78 x 98 cm opening, so a new window fits the old hole.
Sources
- VELUX: roof window sizes and size guide
- VELUX: catalogues (UK price list, July 2026)
- VELUX: finding your window's type sign
- FAKRO: product catalogue (August 2026)
- Keylite: roof window comparison chart
- GOV.UK: Approved Document B, Volume 1 (fire safety in dwellings)
- GOV.UK: Approved Document L, Volume 1 (conservation of fuel and power)
- Makers' sizes checked on 30 October 2026. VELUX, FAKRO and Keylite are trade marks of their owners.
Written by Chris Kervin, Co-Founder, Less.co.uk
Last updated: