How to Read Velux Skylight Sizes So You Order the Right Unit the First Time

Velux skylight sizes look simple on a product page: a code such as M06 and two millimetre figures. The trouble starts when that figure gets treated as the hole in the ceiling. It isn’t, and that one mix-up causes plenty of “it doesn’t fit” moments on site. Before you add a skylight to your cart, it pays to know what the numbers measure, which size family suits your room, and why the flashing matters as much as the window itself. 

Renovation work is keeping plenty of Australian roofs busy. The ABS reported roughly $1.28 billion of residential alterations and additions approved nationally in August 2026, seasonally adjusted (ABS Building Approvals, Australia, August 2026). If a skylight is part of your project, here is how to get the order right first time. 

What Velux skylight sizes actually measure 

There are really four measurements in play, and each one does a different job: 

• The stated size (the listing figure): for the pitched roof range (FS, VS, VSE and VSS), Velux technical data lists this as the external frame, width by height. A VS C04 is 550 x 980 mm. 
• The rough opening: the hole your builder cuts and frames. Velux size guides show it slightly smaller than the outside frame, so the frame sits on the roof deck rather than dropping through it. 
• The flashing footprint: the finished weatherproofing around the unit. It is bigger than both of the above and changes with your roof profile. 
• The glass or daylight area: smaller again. Velux publishes a daylight area figure for each size code, which is handy when comparing two options for the same room. 

The golden rule: order by size code, not by millimetres. The code ties the window, the flashing and the blind together, so everything lines up. 

Decoding Velux skylight dimensions by size family 

On the pitched roof range, the letter tells you the width and the number tells you the length. Here is how the families on our store break down: 

• C family, 550 mm wide: C01 (700 mm), C04 (980 mm), C06 (1180 mm), C08 (1400 mm). Good for hallways, ensuites, laundries and tight roof spaces. 
• M family, 780 mm wide: M02 (780 mm), M04 (980 mm), M06 (1180 mm), M08 (1400 mm). A popular middle ground for kitchens, bedrooms and living areas. 
• S family, 1140 mm wide: S01 (700 mm) and S06 (1180 mm). Wide units for open-plan rooms where you want a big sweep of light. 

Flat roof models work differently. The fixed FCM and solar opening VCS units use a four-digit code, for example 3030 (870 x 870 mm), 3046 (870 x 1275 mm) and 4646 (1275 x 1275 mm). These sit on a raised curb, so the curb size is what you build to. 

Size family	Width (mm)	Lengths available (mm)	Typical use
C (C01, C04, C06, C08)	550	700, 980, 1180, 1400	Hallways, ensuites, laundries
M (M02, M04, M06, M08)	780	780, 980, 1180, 1400	Kitchens, bedrooms, living areas
S (S01, S06)	1140	700, 1180	Open-plan and wide rooms
Flat roof (FCM, VCS)	870 to 1275 (by code)	e.g. 3030, 3046, 4646	Flat and low-pitch roofs

For exact rough opening figures per code, check the current Velux AU size chart before anyone picks up a saw. 

Fixed skylight or opening: which type suits the room? 

Size is half the decision. The other half is whether the skylight needs to open. 

• Fixed skylight (FS and FCM): light only, no ventilation. Ideal for hallways, stairwells and living areas, and the most budget friendly option. Browse the fixed Velux skylights range. 
• Manual opening (VS): opened by hand, so it suits skylights within easy reach. 
• Electric (VSE): wired operation with a rain sensor that closes the skylight when rain is detected. You will need an electrician for the connection. 
• Solar (VSS for pitched roofs, VCS for flat roofs): a solar panel charges a battery, so there is no mains wiring. Also fitted with a rain sensor. A strong choice for retrofits and hard-to-reach ceilings. 

Price generally steps up in roughly that order, and with size within each type. On flat roofs, for example, the Velux VCS 3030 solar opening skylight (870 x 870 mm) is the smaller option, while the Velux VCS 3046 solar opening skylight (870 x 1275 mm) gives you a longer opening and more light. Check each product page for current pricing. 

Think about the room, too. Bathrooms, laundries and kitchens usually earn an opening unit because they need to vent heat and steam. A Melbourne summer under a dark metal roof makes that difference very noticeable. 

Why the skylight flashing kit is matched to your roof, not just your window 

This is where a lot of orders come unstuck. For the pitched roof range, the flashing is sold separately, and it has to match three things: 

• The size code, so it fits the frame exactly 
• Your roof profile, whether that is tiles, corrugated, or a wider rib metal profile such as Trimdeck or Klip-Lok 
• Your roof pitch, because a flashing built for steep roofs will not shed water properly on a low one 

Our custom flashings are listed by size code, with options by roof profile and pitch. Two worked examples: 

• VELUX Custom Flashing C04 (for FS, VS, VSS, VSE 550 x 980 mm), with variants such as corrugated at 15 degrees and over 
• VELUX Custom Flashing M06 (for FS, VS, VSE, VSS 780 x 1180 mm) 

Pitch matters too. Each product listing states the pitch it is designed for, and some opening pitched roof units call for a minimum of 15 degrees. On a lower pitch or a flat roof, an inclined flashing that lifts the unit to the required angle is the usual answer. For a deeper look at profiles, read our guide to roof flashing types for metal, tile and polycarbonate roofs. 

Velux skylight measurements: what to check before you order 

For a new install: 

• Roof pitch (a phone inclinometer app gets you close; confirm on site) 
• Roof profile and sheet or tile type 
• Truss or rafter spacing where the skylight will go, plus any wiring, plumbing or ducting in the way 
• Ceiling height, which sets how deep the light shaft will be 
• What the room needs: light only, or light and fresh air 

For a like-for-like replacement: 

• Look for the size code on the existing frame or in the original paperwork 
• Measure the outside frame, width by height, and compare it against the size chart 
• Measure the opening from inside the roof space as well 
• Check the old flashing; reusing tired flashing on a new window is asking for leaks 

If you pull out an old unit and find a gap around the frame, the original was probably a different size or brand. Don’t fill it with sealant and hope for the best. The opening usually needs re-framing to suit the new size code, which is a job for your builder or roofer. 

Blinds, heat and draughts 

Blinds are easiest to sort at the same time as the skylight. Our Velux FSCH honeycomb and FSLH pleated translucent blinds suit the VS, VSE and VSS range: 

• FSCH honeycomb: the pick for bedrooms and for taking the edge off summer heat 
• FSLH pleated translucent: softens glare while keeping the room bright 
• Both are solar remote, so there is no extra wiring 

If a skylight feels draughty, the unit itself is rarely the culprit. Draughts most often trace back to the installation: gaps around the frame, an unsealed or uninsulated light shaft, or flashing that was not fitted to suit the roof. Once it is in, keep the glass looking its best with our tips on how to clean a skylight window on your roof. 

Your Velux order checklist 

• Size code confirmed (for example C04, M06 or 3046) 
• Opening type chosen: fixed, manual, electric or solar 
• Roof profile and pitch measured 
• Flashing matched to size code, profile and pitch 
• Blind chosen, if you want one 
• Done: ready to order 

Frequently asked questions 

What does the size on a Velux skylight actually mean?
On the pitched roof range, the millimetre figure is the outside frame, width by height. The rough opening is slightly smaller and the flashing footprint is larger. Always order by the size code rather than the millimetres. 

Do all Velux sizes fit between standard trusses?
Not always. Spacing varies from house to house, so measure yours before choosing. The narrower C family suits tighter spacing, while wider M and S units may need the framing altered by a qualified builder. Check the Velux AU installation instructions for your size code. 

Can I replace my old skylight with the same size unit?
Yes, if the old unit has a Velux size code you can match. If it is an older or different brand, compare its outside frame and opening with the size chart first. A gap around the frame usually means re-framing is needed. 

Do I buy the skylight flashing kit separately?
For the pitched roof range, yes. Choose the flashing that matches your size code, roof profile and roof pitch, such as our custom C04 or M06 flashings. 

Are blinds worth adding at install time?
Usually, yes. It is simpler to order everything together, and a honeycomb blind helps manage heat in bedrooms and living areas through Australian summers. 

Still unsure which size or flashing you need? Browse our full Velux skylights range, or call the team in Truganina on (03) 9394 1400 with your size code and roof details. We deliver Australia-wide.