Recessed Light Spacing Calculator
Can light spacing, wall gap, and count from room size.
What it does
Recessed cans spaced by guess leave dark corners or a runway of overlapping circles. A simple half height rule lays an even grid fast, with half spacing to the walls so edges match the middle.
The tool above takes ceiling height with room length and width. It returns light spacing, wall gap, and fixture count in a row grid, in feet or meters.
The defaults light a 12 by 12 ft room with 8 ft ceilings: 4 ft spacing, 2 ft wall gap, 9 cans in 3 by 3. The metric mirror (2.44 m ceiling, 3.66 m room) gives 1.22 m spacing, 0.61 m gap, same 9.
The rule simplifies IES spacing criterion practice for uniform downlighting, where spacing relates to mounting height above the workplane. ENERGY STAR recessed guidance covers the retrofit and install safety half of the job.
How to use
- Pick imperial (feet) or metric (meters).
- Enter ceiling height.
- Enter room length and width.
- Read spacing between cans.
- Read wall gap for the edges.
- Buy the fixture count plus one spare.
Formula
- ceiling
- Floor to ceiling height.
- spacing
- Center to center can distance.
- gap
- Wall to first can distance.
- count
- Rounded grid rows times columns.
Half height is a residential simplification; photometric layouts use IES spacing criterion from LM-79 reports instead. Sloped ceilings, wall wash accents, and tall commercial rooms need their own layouts outside this rule.
Worked example
Example: 8 ft ceiling, 12 by 12 room
Defaults: imperial, 8 ft ceiling, 12 by 12 ft room.
- Spacing: 8 / 2 = 4 ft.
- Wall gap: 4 / 2 = 2 ft.
- Rows: round(12 / 4) = 3 each way.
- Count: 3 x 3 = 9 lights.
- Tool shows 4 ft apart, 2 ft from walls, 9 lights (3 by 3).
- Metric mirror gives 1.22 m, 0.61 m, same 9.
Reference table
| Ceiling | Spacing | Wall gap |
|---|---|---|
| 8 ft | 4 ft | 2 ft |
| 10 ft | 5 ft | 2.5 ft |
| 12 ft | 6 ft | 3 ft |
Limits
- Simplified rule, not a photometric layout.
- Low ceilings under 7 ft need glare care.
- Sloped and accent layouts differ.
- Insulation contact ratings still apply.
Common mistakes
- Even spacing with no wall gap.
- Cramming cans over seating glare zones.
- Mixing color temperatures in one room.
- Skipping IC rating in insulated ceilings.
- Forgetting dimmer compatibility.
Try it yourself
Quick checks. Answers sit tucked under each question.
9 ft ceiling, 18 by 12 room?
4.5 ft spacing, 2.3 ft gap, 12 lights (4 by 3).
Metric 2.44 m ceiling?
1.22 m spacing, 0.61 m gap.
Why half spacing to walls?
Edges then match middle brightness instead of shadowing.
Questions
How far apart recessed lights?
Start at half the ceiling height, then check the room grid.
How far from walls?
Half the spacing, so 2 ft for a 4 ft grid.
How many cans for 12 by 12?
Nine at 8 ft ceilings in a 3 by 3 grid.
Does bulb type change spacing?
Beam angle and lumens shift real layouts; this rule assumes typical downlights.
Kitchen task lighting?
Tighter rows over counters beat the general grid.
IC rated cans needed?
Where insulation touches the housing, yes, plus airtight trims.