Downlight Housing Cut-out & Trim Size Guide (φ35–φ130 mm)
Cut-out set-out is where most downlight problems are created, and almost none of them show up before installation. A hole cut 4 mm oversize looks harmless on the bench and becomes an exposed plaster ring on a finished ceiling. This guide sets out the cut-out and face-ring figures used across our recessed and surface-mounted housing families, the one rule that prevents most of these failures, and the six numbers worth putting on your drawing.
The rule that prevents almost every cut-out failure
Face-ring diameter should exceed the cut-out diameter by at least 10 mm.
That is the figure we quote on wall-wash and recessed fittings, and it is not arbitrary. A ringsaw never cuts a perfect circle, plasterboard flexes when you press the blade into it, and a plasterboard edge can be ragged by a millimetre either way. If the ring only covers the hole by 3–4 mm, any one of those conditions leaves a gap you cannot hide. Ten millimetres of overlap turns three independent tolerances into a non-event.
The corollary matters just as much: the cut-out never has to be perfect, but the ring always has to be generous. When you are specifying, choose the ring first and derive the cut-out from it, not the other way round.
Cut-out, face ring and power by size
The table below covers the recessed families we supply — Convoy narrow-rim, Bauhaus curved, Rome surface COB and the Great-Wall range — grouped by cut-out. Figures are production values; confirm the exact face diameter against the approved sample, because two families can share one cut-out and still differ in ring size.
| Cut-out φ | Face ring φ | Housing height | Typical power | Optic (φ lens · beams) |
|---|---|---|---|---|
| 35 mm | 42 mm | 55 mm | 5–7 W | φ23 · 24° / 36° |
| 45 mm | 52 mm | 65 mm | 7–9 W | φ28 · 24° / 36° |
| 55 mm | 62–75 mm | 55–80 mm | 10–12 W (twin-head: 2 × 5–7 W) | φ35 · 4°/8°/15°/24°/36°/50° |
| 75 mm | 82–98 mm | 74–115 mm | 10–20 W | φ35–φ45 · 15°/24°/36°/50° |
| 95 mm | 98–110 mm | 110–130 mm | 20–35 W | φ55–φ72 · 15°/24°/36°/50°/60° |
| 115–130 mm | 135–145 mm | 125 mm | 35–40 W | φ68 · 15°/24°/36°/50° |
Recessed spotlight and wall-wash families, CRI 97, CCT 2700 / 3000 / 3500 / 4000 / 6000 K. Trim finishes include matt white, matt black, gun-black, bright silver and rose gold, plus the Bauhaus grey / silver / gold trims.
Why the height column matters as much as the diameter
Height is the number buyers forget, and it is the one that stops an installation. A recessed housing is its own heat sink, so the body deepens as the wattage rises: roughly 55 mm at 5 W, 74–80 mm at 12 W, 110 mm at 25–30 W and 125 mm at 40 W.
Add the driver, the wiring and any insulation to the housing height before you check it against the available void. A suspended ceiling with 100 mm of clear space will take a 12 W fitting comfortably and will not take a 35 W one, and discovering that after the grid is up is an expensive afternoon.
Choosing a beam angle from the ceiling height
The optic diameter and beam angle are linked: a larger lens in a larger aperture reaches narrower angles cleanly, which is why the very narrow 4° and 8° spots only appear from the φ35 lens upward.
| Ceiling height | Ambient wash | Accent / display | Narrow spot |
|---|---|---|---|
| 2.4–2.7 m (retail, residential) | 36° – 50° | 24° – 36° | 15° on small apertures |
| 2.7–3.5 m (offices, hotel lobbies) | 36° | 24° | 8° – 15° |
| 3.5–5 m (atria, double height) | 50° – 60° | 24° – 36° | 4° – 15° from φ35 lens up |
Two practical notes. First, wall-wash lenses are asymmetric by design — the beam is shifted to one side to graze a wall evenly — so they are specified by throw distance and spacing, not by a symmetric beam angle. Second, ask for the photometric files (IES or LDT) against the exact optic before you commit a lighting layout; the datasheet beam angle and the delivered beam are not always the same number.
Trim, trimless and surface-mounted: which cut-out applies
- Trim (flanged) housings — a visible face ring covers the cut-out. Use the 10 mm rule and you have margin to spare. This is the right choice wherever set-out is being done by a different trade from the one that finishes the ceiling.
- Trimless plaster-in housings — the housing is installed before the plasterboard is skimmed, and the visible edge is formed by plaster, not by a ring. The cut-out is closer to the body diameter and the tolerance is tighter, so trimless should be set out with the housing physically in hand. Our wall-wash and trimless range ships with installation-depth and cut-out drawings for exactly this reason.
- Surface-mounted housings — there is no cut-out at all. A surface body is fixed to the finished ceiling, which is why it is the correct answer for solid slabs, exposed soffits and retrofit work where the void is too shallow for a recessed body. Bodies in the surface range run from φ55 to φ220 with a power band of 5 to 70 W.
Panel lights are a different cut-out system
Modular panel housings are not set out by diameter but by ceiling module. The standard housings we supply measure 295 × 295, 595 × 595, 295 × 1195 and 595 × 1195 mm, sized to drop into a standard T-grid, with surface frames available for solid ceilings. The cut-out discipline here is about grid alignment and flatness rather than ring overlap — details are on the LED panel light page.
Six numbers to put on your drawing
- Cut-out diameter — with its tolerance, not just the nominal figure.
- Face-ring diameter — the number that actually decides whether the hole is covered.
- Housing height — plus the void you can guarantee on site.
- Power and CCT — and where the driver lives, in the housing or remotely.
- Beam angle and optic — symmetric or asymmetric, with the throw it has to achieve.
- Finish — a RAL reference or an approved physical sample, not a colour name.
Send those six and a section drawing, and tooling feasibility, unit price and lead time can be answered in one round instead of three.
Frequently asked questions
How much bigger should the trim ring be than the cut-out?
As a working rule the face-ring diameter should exceed the cut-out diameter by at least 10 mm. That margin covers the saw kerf, plaster unevenness and normal placing tolerance, so the ring still covers the hole if the cut-out drifts. A ring only 3–5 mm larger will fail on a real ceiling.
What is the standard cut-out for a 2 inch downlight?
A 2 inch (50 mm nominal) recessed spotlight typically uses a 55 mm cut-out with a face ring of roughly 62 to 75 mm, a housing height of 55 to 80 mm and a power band of 10 to 12 W. Confirm the exact figures against the approved sample, because face-ring size varies between families.
Does a trimless downlight use the same cut-out?
No. A trimless plaster-in housing is installed before the plasterboard is finished, so the visible opening is formed by the plaster rather than by a face ring. The cut-out usually matches the housing body rather than being covered by a ring, and the plaster-line tolerance is tighter, so trimless versions should be set out with the housing in hand.
How do I know if there is enough ceiling void for the housing?
Compare the housing height with the available void, then add clearance for the driver, the wiring and any insulation. Recessed spotlight housings in our ranges run from 55 mm to 130 mm high depending on power, and the higher-wattage sizes need proportionally deeper voids because the body doubles as the heat sink.
Related reading: how to choose a downlight housing supplier, manufacturer or trading company, and aluminum versus PC housings.