Recessed Lighting Calculator
Lay out recessed lights for a room: how many, the grid they sit on, the spacing between them and the distance off the walls.
The spacing rule behind the layout
Recessed lights are placed by a simple trade rule: space them about one ceiling height apart, and set the rows half a spacing in from the walls. At an 8 ft ceiling that means lights roughly 8 ft apart and 4 ft off the walls — far enough apart that their cones overlap at counter and table height, close enough that no corner of the room goes dim.
Lights along a wall = room length ÷ ceiling height, rounded to a whole grid · Wall offset = actual spacing ÷ 2
Example: a 16 × 12 ft room with an 8 ft ceiling: 16 ÷ 8 = 2 lights along the length, 12 ÷ 8 = 1.5 → 2 across, so a 2 × 2 grid of 4 lights, spaced 8 ft × 6 ft, sitting 4 ft and 3 ft off the walls.
| Room | Ceiling | Grid | Lights |
|---|
| 12 × 10 ft | 8 ft | 2 × 1 | 2 |
| 12 × 12 ft | 8 ft | 2 × 2 | 4 |
| 16 × 12 ft | 8 ft | 2 × 2 | 4 |
| 20 × 15 ft | 9 ft | 2 × 2 | 4 |
| 24 × 16 ft | 10 ft | 2 × 2 | 4 |
Treat the grid as the ambient layer, not the whole lighting plan. Kitchens and workshops tighten the spacing to about three quarters of the rule and add dedicated task lights over counters and benches; a row over a sink or a picture light does work no ceiling grid can. Keep fixtures out of joist bays you cannot see — before drilling, confirm what is above the ceiling, and use housings rated for insulation contact (IC) wherever insulation will touch them.
Frequently asked questions
How many recessed lights does a 12 × 12 room need?
On the standard rule — 8 ft ceiling, spacing of 8 ft — the grid is 2 × 2, so 4 lights. A kitchen of that size usually adds task lighting over the counters rather than more ceiling lights.
What if my room falls between grid sizes?
The calculator rounds to the nearest whole grid and reports the actual spacing that results, so a 14 ft room on an 8 ft rule gets 2 lights at 7 ft spacing — slightly generous light, evenly spread, which is the right side to err on.
How far from the wall should the first light be?
Half the spacing between lights — that is built into the layout. It keeps the wall wash even and stops the perimeter of the room falling into a dim border.
Do taller ceilings need more lights or brighter ones?
The rule spaces by height, so a 12 ft ceiling spreads the grid wider; each light then needs more output (lumens) to deliver the same light at floor level. Keep the count from the grid and step up the fixture brightness.
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