To find the right cut-out size for lighting in gypsum board, rely on the cut-out size stated in the product specifications—not the fixture's outer diameter. The cut-out is the diameter of the hole you cut in the gypsum so the spotlight or downlight drops in and rests on its outer trim.
Quick answer: On the product box or page, look for "Cut-Out Size," "Ceiling Opening," or "Mounting Hole." The number given (in millimeters) is the hole diameter to cut in the gypsum board.
Outer diameter vs. cut-out size
- Outer diameter: The size of the visible trim above the ceiling.
- Cut-out size: The inner hole cut into the gypsum; always smaller than the outer diameter.
Example: a unit with a 120 mm outer diameter and a 90 mm cut-out means you cut a 9 cm hole in the board.
How to find the size before buying
Check the manufacturer's specifications and look for one of these terms:
- Cut-Out Size
- Ceiling Opening / Ceiling Cut-Out
- Mounting / Installation Hole
It's usually given in millimeters (mm) or centimeters (cm).
Common cut-out sizes
Sizes vary by fixture type; the most common on the market are:
- Mini COB spot: roughly 50–65 mm cut-out.
- Medium spot/downlight: 75–90 mm.
- Standard downlight: 100–110 mm.
- Large downlight: 150–165 mm or more.
Still, the product spec is always the exact reference.
Steps to measure and mark the hole
- Read the cut-out size from the fixture's specs.
- Mark the hole center on the gypsum board.
- Use a hole saw of the same cut-out size, or a compass and a manual cutter.
- Make sure there are no cables or AC ducts behind the spot before cutting.
- Test-fit the unit to confirm the springs grip firmly inside the hole.
Other factors besides the hole size
- Gypsum thickness: Usually 9 or 12.5 mm; make sure the clips fit that thickness.
- Depth behind the ceiling: Leave enough space for the fixture body and cables.
- Spacing between units: Distribute evenly for uniform light.
Common mistakes to avoid
- Using the outer diameter instead of the cut-out size.
- Cutting the hole too large, leaving the unit loose.
- Skipping the cable check behind the ceiling before cutting.
Frequently asked questions
What is the most common spotlight cut-out size?
Often 75–90 mm for a medium spot, but always check the product spec.
Can I enlarge the hole if it's too small?
Yes, carefully with the right cutting tool—but shrinking an oversized hole is difficult.
What if the hole is bigger than the fixture?
Use a converter ring or a fixture with a larger outer trim to cover the hole.
Conclusion
The key to gypsum-board lighting is using the cut-out size from the product spec, a matching hole saw, and accounting for gypsum thickness and depth behind the ceiling. That gives you a snug fit and a clean finish.
Shop spotlights and downlights in various sizes at Tirtk Lighting & Electrical
Related: Shop downlights and spotlights at Tirtk.