Downlight spacing calculator
A no-nonsense downlight spacing calculator: type in the room, get the grid, the spacing and the wall distances. Plus lumens guidance so the room is actually bright enough.
- Spacing (length × width)–
- Distance from walls–
- Grid–
Guidance only. The height ÷ 2 rule is a layout starting point, not a lighting design. Beam angle, lumen output, joist positions and where the worktops and mirrors are all move the answer.
How to work out downlight spacing (and how many you need)
Every electrician has a version of this rule, and the one that works is beautifully simple: spacing between downlights = ceiling height ÷ 2, and distance from the walls = half the spacing. On a standard UK 2.4 m ceiling that gives you 1.2 m between fittings and 0.6 m from the walls. That wall gap matters more than people think, get it wrong and you scallop light down the walls or leave a gloomy border round the room.
The calculator above does exactly that, then snaps the result to a tidy, symmetrical grid, because "3.17 downlights across" is no use to anyone holding a hole saw.
Plan the whole layout in five steps
- Measure the room: length, width and ceiling height.
- Divide the ceiling height by two. That is your spacing between fittings, and half of it again is your distance from the walls.
- Snap to a symmetrical grid and count the fittings, or let the calculator above do steps 2 and 3 for you.
- Multiply the floor area by the lumens target in the table below, then check the combined output of your fittings clears it. Falls short? Pick brighter fittings, not more holes.
- Adjust for the real room: shift fittings over worktops and desks, dodge the joists, and check bathroom zones before you order anything.
Spacing gets you the layout. Lumens get you the light.
A perfect grid of underpowered fittings is still a dim room. Once you have the count, check the total output against what the room is for:
| Room | Aim for (lumens per m²) | Feel |
|---|---|---|
| Kitchen | 300+ | Bright task lighting |
| Bathroom | 250-300 | Bright and even |
| Living room | 150-200 | Relaxed, dimmable |
| Bedroom | 150 | Soft |
| Hallway | 100-150 | Welcoming |
| Home office | 300+ | Focus |
A quick worked example
Take a 4 m × 3.5 m kitchen with a 2.4 m ceiling. The rule gives roughly 1.2 m spacing, which snaps to a 3 × 3 grid, so 9 fittings. At 600 lm each that is 5,400 lm over 14 m², which works out at 386 lm/m². Comfortably past the 300 lm/m² target, so it is nicely bright for a kitchen without turning the place into an operating theatre.
Beam angles, the two-minute version
The beam angle is how wide the cone of light spreads from the fitting, and the lighting retailers write essays about it. Here is what actually matters. Most standard downlights ship at around 38 degrees, which suits general lighting on a normal 2.4 m ceiling. The published angle is where the beam drops to half strength, useful light carries on beyond it, which is why sensible spacing gives you even coverage rather than a row of spotlit circles on the floor.
| Beam angle | Best for |
|---|---|
| Narrow (25 degrees or less) | Accent lighting: artwork, alcoves, feature walls |
| Medium (roughly 36 to 45 degrees) | The standard choice for general rooms at 2.4 m |
| Wide (60 degrees plus) | Soft, even, shadow-free light, and lower ceilings |
Taller ceilings spread each beam wider but dilute it, so on a 3 m ceiling either step up the lumens or tighten the beam a touch. And mixing angles in one room is allowed: wide beams for the general grid, a couple of narrow ones on the picture wall.
The bits the rule of thumb won't tell you
- Joists win, every time. Shift a fitting under 100 mm to miss one rather than notching structure to keep a "perfect" grid. Nobody stands in the room with a tape measure afterwards.
- Put task light where the tasks are. Over the worktops, over the hob, over the desk, not in the middle of the floor where it lights the back of your head.
- Bathrooms need the right IP rating for the zone. Check the bathroom electrical zones guide for where the zones fall, and run any fitting through the IP rating checker before you buy a box of ten.
- Most plasterboard ceilings need fire-rated fittings, they restore the fire compartment you just cut a 70 mm hole through.
- Dimmable LEDs on a decent driver beat cramming more fittings in. Flexibility wins over raw count.
One last sense check: modern LED downlights sip power, so a whole ceiling of them usually sits happily on a lighting circuit. If you are adding a serious number, or mixing in transformers and drivers, run the load through the watts to amps calculator before you sign the circuit off.
Downlight spacing FAQs
How many downlights do I need?
Start with the calculator's grid: roughly one fitting every 1.2 to 1.5 m in each direction on a standard 2.4 m ceiling, outer row at half that from the walls. Then check the total lumens against the table above. If the count passes the spacing test but fails the lumens test, pick brighter fittings, not more holes.
How far should downlights be from the wall?
Half your spacing, so about 0.6 m at standard ceiling height. That keeps the light even to the edges of the room without harsh scalloping. The exception is deliberate wall-washing: go closer, around 300 to 400 mm, when you want light down over kitchen worktops or a feature wall.
What spacing for a 2.4 m ceiling?
About 1.2 m between fittings. That is the height divided by two, and it is the number this whole trade rule is built around because 2.4 m is the standard UK ceiling. Taller ceilings spread further apart, a 3 m ceiling gives you 1.5 m spacing.
Do downlights need to be fire rated?
In most plasterboard ceilings, yes. The ceiling is a fire barrier, and every hole you cut compromises it. A fire-rated downlight has an intumescent liner that seals the hole in a fire and restores the compartment. Given the price difference is pennies these days, fitting anything else in a habitable building is a false economy.
What IP rating do bathroom downlights need?
IPX4 minimum in zones 1 and 2, which covers splashing water. In practice, IP65 fittings are the easy safe pick: they cover every zone, they cost barely any more, and you never have to think about which fitting went where. Check the bathroom zones guide if you are not sure where zone 2 ends.
Can I have too many downlights?
Absolutely, and half the ceilings in Britain prove it. The Swiss cheese look: fittings everywhere, glare from every angle, and a plasterboard ceiling with more holes than board. Fewer, brighter, well-placed fittings on a dimmer nearly always give a better result for less money and less making good.
What beam angle should I choose for downlights?
Around 38 degrees is the default for general lighting on a standard 2.4 m ceiling, and it is what most fittings ship with. Go wide, 60 degrees plus, for soft even light or lower ceilings, and narrow, 25 degrees or less, for accents like artwork and feature walls. Mixing them in one room is fine: wide for the grid, narrow for the features.
Can I cover downlights with loft insulation?
Only if the manufacturer says you can. Some fire-rated LED downlights are approved for insulation contact, and it will say so in the fitting's instructions. If it does not, keep the insulation clear as directed or fit a proper downlight cover. Heat has to go somewhere, and a downlight cooking under a duvet of loft roll fails early at best. Check before the insulation goes down, not after.
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