Sizes of Can Lights | Match the Cut-Out, Not the Trim

Recessed “can” lights are sized by the ceiling cut-out diameter, with 4-inch, 5-inch, and 6-inch being the standard residential sizes.

For the full breakdown, see our best 2″ Can Lights guide.

Most of the time, a “can light” is a recessed fixture, and the number you see on the box refers to the inside housing diameter or the hole cut in your ceiling, not the size of the visible trim ring. The most common sizes for home use are 4-inch, 5-inch, and 6-inch, with the 6-inch size being the standard for general-purpose lighting. Knowing which one you have is the difference between a ten-minute swap and a frustrating trip back to the store.

Sizing a Recessed Light Fixture

To find the size of a recessed light, you measure the diameter of the ceiling cut-out or the inside of the housing. The visible trim is often wider than the housing, so measuring the trim is the most common mistake people make and it results in buying the wrong replacement. The sizes most often referenced for US homes are 4-inch, 5-inch, and 6-inch fixtures.

When you measure the actual opening, you’ll usually find it’s a little larger than the nominal size name. Common residential cut-out sizes are roughly:

• 4-inch can: about a 4-3/8-inch cut-out
• 5-inch can: about a 5-5/8-inch cut-out
• 6-inch can: about a 6-3/8-inch cut-out

Which Size Do You Need?

No single size works everywhere. The right choice depends on the room’s purpose, its ceiling height, and the amount of light you want to spread. Four-inch and 5-inch fixtures are common choices for kitchens and task lighting, where you want focused light on a counter or workspace. The 6-inch fixture is the most common for general lighting in living rooms, hallways, and bedrooms because it produces a broader pool of light.

For larger spaces, you might find 7-inch to 9-inch fixtures, which give a wider wash of light and are used more often in big rooms or commercial settings. These larger sizes are rarely needed in typical homes.

Compatibility and Common Mistakes

Most people searching for can light sizes are trying to replace a bulb, trim, or the whole retrofit module. It’s important to remember that the nominal size on the housing is an approximate label, and exact dimensions vary by manufacturer. A 6-inch housing from one brand may be a fraction of an inch different from another, so it’s never safe to assume all “6-inch” fixtures are interchangeable.

When shopping for LED retrofit kits, you’ll frequently see modules sold as “5/6-inch” compatible. This means the module’s design fits both 5-inch and 6-inch housings, which covers a lot of common home installations.

There is also a growing category called “canless” recessed lights. These do not have a metal housing at all, so their size is determined entirely by the ceiling cut-out. That’s an important distinction if you’re swapping out an old fixture for a new canless design.

How to Measure Your Existing Can Light

Here’s the most reliable way to identify your can light’s size before you buy anything:

1. Remove the trim or LED module if it’s detachable.
2. Measure the inside diameter of the housing or the raw cut-out in the ceiling.
3. Round to the nearest common size, which for residential cans is usually 3, 4, 5, or 6 inches.
4. Match your replacement to that nominal size and any stated compatibility range (like 5/6-inch).

After you know your size, a final consideration is location. Bathrooms and shower areas require moisture-resistant or wet-rated fixtures, and if your ceiling space is shallow, you’ll need a low-profile housing rather than a standard one. Home Depot’s recessed lighting buying guide and Lowe’s recessed lighting buying guide both emphasize matching the fixture to your ceiling height and room size, not just picking a number out of the air.