What size roof lantern do I need?
Standard roof lantern sizes from 1000 × 1000 mm to 3000 × 4000 mm, how to choose one for your room and when made-to-measure is worth it.
There is no single right size, but there is a sensible process: start from the room, check the glazing allowance, then fit the nearest standard size to the roof structure. Lanterns are always described by the external kerb size, width first.
How big should a lantern be for my room?
Designers often aim for the lantern to cover roughly a sixth to a quarter of the floor area it lights, within the overall glazing limits below, leaving a solid border for downlights, structure and a neat plaster return. Over a dining table, a lantern a little larger than the table works well. Over a kitchen island, align the lantern's long axis with the island.
Standard sizes and guide prices
| Kerb size | Roof area | Guide price | Configure |
|---|---|---|---|
| 1000 × 1000 mm | 1.00 m² | £1,095–£1,295£912 ex VAT from | Configure |
| 1200 × 1200 mm | 1.44 m² | £1,295–£1,495£1,079 ex VAT from | Configure |
| 1000 × 1500 mm | 1.50 m² | £1,295–£1,495£1,079 ex VAT from | Configure |
| 1000 × 2000 mm | 2.00 m² | £1,495–£1,795£1,246 ex VAT from | Configure |
| 1000 × 2500 mm | 2.50 m² | £1,795–£2,095£1,496 ex VAT from | Configure |
| 1000 × 3000 mm | 3.00 m² | £1,995–£2,295£1,662 ex VAT from | Configure |
| 1500 × 1500 mm | 2.25 m² | £1,595–£1,895£1,329 ex VAT from | Configure |
| 1500 × 2000 mm | 3.00 m² | £1,995–£2,295£1,662 ex VAT from | Configure |
| 1500 × 2500 mm | 3.75 m² | £2,295–£2,695£1,912 ex VAT from | Configure |
| 1500 × 3000 mm | 4.50 m² | £2,595–£2,995£2,162 ex VAT from | Configure |
| 2000 × 2000 mm | 4.00 m² | £2,395–£2,795£1,996 ex VAT from | Configure |
| 2000 × 3000 mm | 6.00 m² | £3,195–£3,695£2,662 ex VAT from | Configure |
| 2000 × 4000 mm | 8.00 m² | £4,095–£4,795£3,412 ex VAT from | Configure |
| 2500 × 4000 mm | 10.00 m² | £4,895–£5,695£4,079 ex VAT from | Configure |
| 3000 × 4000 mm | 12.00 m² | £5,695–£6,595£4,746 ex VAT from | Configure |
Guide prices include VAT at 20%, supply only, aluminium with self-cleaning double glazing in a stock colour. Your fixed price is confirmed in writing on your quote before you order.
What about the 25% glazing guideline?
In England, building regulations guidance for extensions generally expects windows, rooflights and glazed doors together to stay within 25% of the extension's floor area plus the area of any openings the extension covers. A 4 × 5 m extension (20 m²) has an allowance of about 5 m² plus covered openings, and a big set of bifolds can use most of it. Your designer can use energy calculations to justify more glass; Wales, Scotland and Northern Ireland have their own rules.
When is made-to-measure worth it?
- Your kerb already exists and is not a standard size.
- The structure dictates an exact opening, for example between steel beams.
- You want a particular proportion, bar layout or vent position.
Otherwise, choosing a standard size and building the kerb to suit is usually quicker and cheaper.
Sources
Written by the Buy Roof Lanterns team. Last reviewed 19 October 2026. General guidance only; your designer, building control body or council confirms what applies to your project.