Why Can’t I Find My Downlight Cutout Size? Why Are They All Now 90mm?

If you’ve tried replacing a downlight lately, you’ve probably run into a frustrating problem - none of the new fittings seem to match your old ceiling cutouts. The sizes have changed, and almost everything now seems to be 90mm. So what happened?

The Shift to Standardisation

Over the last few years, lighting manufacturers have moved toward standardising downlight cutouts around 90mm. This makes installation simpler for electricians and helps reduce confusion across brands. The 90mm size has effectively become the “universal” size for modern LED downlights in Australia.

That’s great for new installs - but not so great if your home was built during one of the many “in-between” size eras. Old halogen fittings and early LED models came in all sorts of diameters: 70mm, 75mm, 80mm, 92mm, even 95mm. Every manufacturer had their own idea of “standard.”

Why Old Sizes Disappeared

As LED technology improved, manufacturers redesigned their fittings from the ground up. Heat sinks got smaller, drivers became more efficient, and lighting output increased dramatically. When these designs were refreshed, brands took the opportunity to align with the 90mm cutout standard - meaning most of the old-size housings simply stopped being produced.

Lighting models also change fast. What was a best-seller five years ago might have been replaced by three generations since. Even if the look is similar, the physical design often isn’t - so matching an older fitting exactly is nearly impossible.

What You Can Do

If your cutouts are smaller than 90mm, you have two options:

• Enlarge the hole using a hole saw or plaster rasp to fit a modern 90mm model.

• Use a conversion plate (also called a “retrofit ring” or “cover plate”). These hide the old cutout and let you install a smaller modern fitting neatly.

If your cutout is larger than 90mm, there are a few “oversized” downlights on the market, but options are limited. In most cases, a conversion plate is the simplest and cleanest solution.

The Bright Side

Once you move to a modern 90mm LED downlight, you’re set for the long term. It’s now the industry standard - meaning replacements will be easy to find for years to come. You’ll also benefit from better efficiency, higher CRI, selectable colour temperature, and much longer lifespans.