Downlight Cut Out Size: What to Measure Before You Replace One
Last updated: 12 October 2026
Quick answer: A downlight’s cut-out size is the diameter of the hole in the ceiling that the light fits into; for a square or rectangular light, it is the length of each side. It is smaller than the visible face of the light, which has to cover the edge of the hole. To replace a downlight, measure the hole itself and choose a light whose listed cut-out matches it, then check that the light’s depth fits the space above your ceiling.
The three sizes on a downlight listing
Only the cut-out, also called the hole size, has to match your hole. The other two sizes decide how the light looks and whether it fits above the ceiling.
| Size | What it is | What it decides |
|---|---|---|
| Cut-out (hole size) | The opening in the ceiling that the light is pushed into | Whether the light fits your hole |
| Overall (outer) diameter | The width of the visible face of the light; for a square light, the length of each side | Whether the face covers the edge of the hole |
| Depth | How far the body of the light reaches above the ceiling surface | Whether it fits in the space above the ceiling |
Labels vary. Our product pages call the hole “Cut-out”, “Cut Out Size” or “Cut Size”, the face “Outer Diameter”, “Surface Size” or “Product Size”, and the depth “Height” or “Thickness”.
How to measure the hole when replacing a downlight
Measure the hole in the ceiling, not the rim of the old light, because the rim hides the real edge of the hole.
- Switch off the power. Turn the light off at the switch and switch off its circuit at the distribution board.
- Take the old light down. Lower it gently and do not pull on the wires. If it is wired directly, ask a professional installer to disconnect it; the shipping note on our product pages says “Installation should be performed by a qualified electrician.”
- Measure the hole. Use a tape measure in millimetres and read across the hole at its widest point. For a square or rectangular hole, measure each side. If the hole is not a clean shape, note both the widest and the narrowest reading.
- Check the space above. Slide the tape through the hole to see how much clear room there is above the ceiling before something blocks it, such as a pipe or a beam.
- Take a photo. Photograph the hole with the tape measure across it so the number can be read.
Cut-out sizes on some of our recessed lights
Cut-out figures differ a lot between recessed lights, from 80 mm to 200 mm in the table below (and more in our downlight range), so compare the figure itself, not the wattage or the product name. Figures are as listed on each product page on 12 October 2026; a dash means no figure to quote here.
| Product | Cut-out | Overall size | Depth |
|---|---|---|---|
| Philips LED Recessed Downlight 15W (Round) | ~175 mm | β | β |
| Lighting Hub DOB Downlight 18W (Round) | 185-200MM | Surface Size 222MM | β |
| Square Recessed Downlight T2301 (White / Black) | 80 x 80 mm | Product Size 93 x 93 mm | Thickness 47 mm |
| Double Adjustable Recessed Spotlight (GU10 x 2) β DL-5602 | 160 x 80 mm | Length 180 mm, Width 92 mm | β |
| Recessed Spotlight Housing | 80mm | Outer Diameter 88mm | Height 50mm |
Where a row gives both, the overall size is larger than the cut-out, because the face covers the edge of the hole. The Philips 15W listing also lists five sizes: 6W (4 inch) ~100 mm, 9W (5 inch) ~125 mm, 12W (6 inch) ~150 mm, 15W (7 inch) ~175 mm and 19W (8 inch) ~200 mm. Some listings give a range, as the DOB 18W does with 185-200MM, so check that your hole falls inside it.
If the hole and the new light do not match
If your hole is smaller than the listed cut-out, the light may not go in; if it is larger, the light goes in but may sit loose or leave a gap around its face.
- Hole slightly bigger than the cut-out: choose the next larger cut-out, or a light made for a flexible opening, such as the Lighting Hub Adjustable Downlight 15W (Round), whose listing describes a “flexible cut-out design”; ask us whether it suits your hole. A trim ring, a flat ring that covers the gap, can hide a small difference.
- Hole smaller than the cut-out: choose a light with a smaller cut-out. Making a hole bigger is ceiling work, so ask whoever built or fitted your ceiling.
- Rectangular or odd-shaped hole: match the shape as well as the size. A rectangular hole such as the 160 x 80 mm cut-out of the DL-5602 needs a light made for that shape, because a light with a round cut-out will not suit it.
GU10 housing or all-in-one light
A GU10 fitting is a housing that takes a separate GU10 bulb, while an all-in-one downlight has the LED built in; the hole is measured the same way for both. The DL-5602 listing says “Lamp Type: GU10 x 2” and “Bulbs are not included”. The T2301 lists “Lamp Type: GU10 x 1” and “Compatible with GU10 bulb (1 unit)”, so ask us whether a bulb comes with it.
GU10 bulbs have two short pins and twist to lock; our light bulb base types guide explains how GU10 differs from E27 and the other bases. Fittings like these sit in our Spotlight range, and our downlight vs spotlight guide explains how spotlights differ from downlights.
If there is not enough room above the ceiling
If the light is deeper than the clear space above your ceiling, choose a surface-mounted light, which is fixed to the ceiling and needs no hole. Compare the depth on the listing with the space you measured; the T2301, for example, lists “Thickness: 47 mm”. A GU10 bulb and its holder may need more room than that, so if space is tight, or a listing gives no depth, ask us before you order. The GU10 Surface Mounted Downlight Fitting β Single Head (White / Black) listing says “Surface Mounted Design β No need ceiling cut-out”, and CEILING LIGHT MODEL 2531/400 (White) 26W in our Ceiling Light range lists “Installation: Surface Mounted Ceiling Light”. When you replace a recessed light with a surface-mounted one, the old hole is still there, so choose a fitting wide enough to cover it or have the hole patched first.
Send us a photo before you buy
Start from our installation service page: message us on WhatsApp or use the enquiry form, then send a photo of your hole with the tape measure across it. The page also asks for the ceiling height and ceiling type, and covers lights, new or replacement. If you are changing the layout, send your floor plan too, and our light specialist can assess it and recommend how many fittings each space needs; our guide to how many downlights you need covers the sums. You can also compare sizes at one of our 5 showrooms; call the branch first to check what is on display.
FAQ
What is the cut-out size of a downlight?
The cut-out size is the diameter of the hole in the ceiling that the downlight fits into; for a square or rectangular light it is the length of each side, such as 80 x 80 mm on the Square Recessed Downlight T2301 listing. It is smaller than the light’s visible face, which covers the edge of the hole.
What is the difference between a downlight’s cut-out and its diameter?
The cut-out is the hole in the ceiling, while the diameter (listed as Outer Diameter, Surface Size or Product Size) is the width of the visible face, which is larger. Depth is a third figure: how far the light reaches above the ceiling. On the Recessed Spotlight Housing listing, the cut-out is 80mm, the outer diameter is 88mm and the height is 50mm.
How do I measure a downlight hole when replacing one?
Switch off the power at the switch and the distribution board, take the old light down (ask a professional installer to disconnect it if it is wired directly) and measure across the hole in millimetres at its widest point. For a square or rectangular hole, measure each side. Then send us a photo with the tape measure across the hole.
What if my ceiling hole is bigger or smaller than the new downlight?
If the hole is smaller than the listed cut-out, the light may not go in, so choose a smaller cut-out. If it is larger, the light may sit loose or leave a gap, so choose the next larger cut-out, a light made for a flexible opening, or add a trim ring.
Does a higher-wattage downlight need a bigger hole?
It can. On the Philips LED Recessed Downlight listing, the cut-out rises from about 100 mm at 6W to about 200 mm at 19W, and the Lighting Hub DOB Downlight 18W listing shows 145-155MM for 12W and 185-200MM for 18W. Brands and ranges differ, so compare the cut-out figure, not the wattage.
Written by the Lighting Hub team, Since 2009.
