How to Choose the Correct Downlight Cut-Out Size
Choosing the right downlight isn't just about wattage, colour temperature or style. The cut-out size is one of the most important measurements to get right, especially when replacing existing downlights.
This guide explains how to measure a downlight cut-out, how to match a new fitting to an existing ceiling hole and what you need to know about fire-rated downlights.
Correct Fit
Match the fitting to the ceiling opening for a secure installation.
Secure Installation
The correct cut-out allows the spring clips to hold the fitting properly.
Neater Finish
A correctly sized opening helps the bezel sit neatly against the ceiling.
Fire Rating
Where required, select a fire-rated fitting suitable for the ceiling construction.
What is a downlight cut-out size?
The cut-out size is the diameter of the hole in the ceiling that the body of the downlight passes through.
It is not the same as the overall diameter of the bezel. A downlight may have a 90mm visible face while requiring a considerably smaller ceiling opening.
Manufacturers normally list the required cut-out in millimetres, for example Ø 70mm or Ø 72–75mm.
Measure the ceiling opening
← CUT-OUT DIAMETER →Measure directly across the widest point of the circular ceiling hole.
How to choose the correct cut-out size
Check the specification
Look at the product page or datasheet and find the manufacturer's specified cut-out measurement.
Measure the existing hole
If you're replacing a downlight, remove the old fitting and measure the diameter of the ceiling opening.
Match the measurements
Choose a fitting whose stated cut-out size matches your ceiling opening as closely as possible.
Check the bezel coverage
The bezel must be larger than the ceiling hole so it fully covers the opening and provides a clean finish.
Typical downlight cut-out sizes
Downlights are available in many different dimensions, so the table below should only be used as a general guide.
| Approx. Downlight Face Size | Typical Cut-Out Range | Common Applications |
|---|---|---|
| 68–80mm | Ø 55–70mm | Compact fittings, bathrooms, hallways and accent lighting |
| 90–100mm | Ø 75–90mm | Kitchens, bedrooms and general domestic lighting |
| 110–120mm | Ø 90–105mm | Larger downlights and general room lighting |
| 150–180mm | Ø 120–160mm | Larger spaces and selected commercial installations |
| 200mm+ | Ø 160mm+ | Commercial and specialist feature lighting |
What is a fire-rated downlight?
Cutting a hole into a fire-resisting ceiling can affect the performance of that ceiling. A fire-rated downlight is designed and tested to help maintain the required fire resistance of the ceiling system when it is installed correctly.
Helps Maintain Fire Resistance
Fire-rated fittings are tested as part of specified ceiling constructions to help limit the passage of fire through the opening.
Check the Required Rating
Products may be tested for different fire-resistance periods, commonly including 30, 60 or 90 minutes.
Check Ceiling Compatibility
The fire rating must be suitable for the particular ceiling construction and installed exactly as specified by the manufacturer.
When should you consider fire-rated downlights?
Fire-rated downlights are particularly important where recessed fittings penetrate a ceiling that forms part of a required fire-resisting construction. The exact requirement depends on the building, location, ceiling system and applicable building regulations.
Check the product for:
- Declared fire-resistance rating
- Compatible ceiling construction
- Required installation clearances
- Manufacturer's installation instructions
- Any additional insulation-cover requirements
Don't assume:
- Every downlight is fire rated
- Every ceiling requires the same rating
- A 90-minute fitting is suitable for every ceiling
- Fire rating and IP rating mean the same thing
- All fire-rated products are tested in identical constructions
Before you cut the ceiling
Check the ceiling
- Confirm the required cut-out diameter
- Check for joists above the intended position
- Check for pipes and electrical cables
- Confirm sufficient ceiling void depth
- Check any insulation requirements
Check the fitting
- Confirm the cut-out size from the datasheet
- Check the overall bezel diameter
- Check whether fire rating is required
- Check bathroom/IP requirements where applicable
- Follow the manufacturer's installation instructions
What if the existing ceiling hole is too large?
This is common when replacing older downlights. If the existing opening is larger than the cut-out required by your new fitting, its spring clips may not grip securely and the bezel may not fully cover the hole.
Look for a downlight with a larger or adjustable cut-out range, or a compatible conversion plate or oversized bezel where the manufacturer offers one. Avoid relying on an insecure fitting simply because the bezel appears to cover the opening.
Frequently asked questions
What does downlight cut-out size mean?
It is the diameter of the ceiling hole required for the body of the downlight to pass through. It is normally specified in millimetres.
Is cut-out size the same as downlight diameter?
No. The visible bezel or face of the downlight is normally larger than the cut-out because it needs to cover the edge of the ceiling opening.
How do I measure an existing downlight hole?
With the existing fitting safely removed, measure directly across the widest part of the circular ceiling opening. Measure the hole itself, rather than the old fitting or bezel.
Are all downlights fire rated?
No. Check the individual product specification. Where a fire-rated downlight is required, also confirm that its tested rating is appropriate for the ceiling construction.
What do 30, 60 and 90 minute fire ratings mean?
They refer to fire-resistance periods achieved under specified test conditions and ceiling constructions. Always confirm which construction and rating are required for the installation.
Is fire rating the same as an IP rating?
No. Fire rating relates to fire resistance of the ceiling assembly, whereas an IP rating describes the fitting's level of protection against ingress of solid objects and water.
Need help choosing your downlights?
Browse our range of LED, fire-rated and bathroom downlights or speak to the Electricals Online team for help choosing the right fitting.