Recessed lights for a 18 × 30 ft bathroom with a 10 ft ceiling
| Layoutacross the 18 ft dimension × along the 30 ft dimension | 4 × 6 |
|---|---|
| Spacing (rule of thumb)half of the 10 ft ceiling | 5ft |
| Actual spacing to mark outafter rounding to whole fixtures | 4.5 × 5ft |
| First light from the wallhalf a spacing — closer washes the wall, further leaves dark corners | 2.3 × 2.5ft |
| Room area | 540ft² |
| Target light levelgeneral light — the mirror needs light from the sides, not above | 30fc |
| Total lumens needed | 16,200lm |
| Lumens per fixtureabout 9 W each in LED | 675lm |
- Room width
- 18 ft
- Room length
- 30 ft
- Ceiling height
- 10 ft
- Room
- bathroom
The grid
Spacing for recessed cans is ceiling height divided by two. A 10 ft ceiling gives 5 ft, which across a 18 × 30 ft room works out to a 4 × 6 grid — 24 lights.
Rounding to whole fixtures moves the real spacing to 4.5 × 5 ft. Mark the ceiling off those numbers, not off the rule of thumb. The first row sits 2.3 ft from the wall — half a spacing. Closer and you get a bright band down the wall; further and the corners go dark.
What to buy, not just how many
540 ft² at 30 footcandles needs 16,200 lumens in the room, which is 675 lumens per fixture — around 9 W in LED.
That is the number to shop by, and it is the one most layout calculators leave out. A 4″ LED downlight typically runs 600–800 lm; a 6″ runs 800–1,200 lm.
Before you cut
Find the joists first. A 4 × 6 grid rarely lands clear of framing on the first attempt, and shifting a can six inches to miss a joist is invisible once the trim is on. Put the whole layout on a dimmer while the wiring is open — it costs almost nothing then and cannot be added cheaply later.
Notes
- The spacing rule is ceiling height ÷ 2, which gives 5 ft here. Rounding to whole fixtures moves it to 4.5 × 5 ft — mark the ceiling off the real numbers, not the rule.
- 675 lumens per can is the figure to shop by. A 4″ LED downlight typically runs 600–800 lm and a 6″ runs 800–1,200 lm, so either size covers it.
- Bathroom is a task space. 30 fc is the general level — countertops, desks and mirrors still need their own light. Ceiling cans alone put the light behind you and your own shadow onto the work.
- Put them on a dimmer. It costs almost nothing at install, and it is the difference between a ceiling that works at dinner and one that works at 11pm.
- Check the joists before marking. A 4 × 6 grid rarely lands clear of framing on the first try, and moving a can 6 inches to miss a joist is invisible once the trim is on.
Nearby sizes
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Read more
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