About the Recessed Lighting Layout Calculator
This recessed lighting calculator plans an even grid of recessed (can or wafer) lights for a room. Enter the room length and width, the ceiling height, the brightness you want and the lumen output of the fixtures you plan to buy. It returns the number of lights, the rows and columns, the spacing between fixtures and how far the first row sits from each wall.
Spacing starts from the widely used rule of thumb of about half the ceiling height between fixtures (4 ft apart on an 8 ft ceiling) with the outer lights half a spacing from the walls, which gives even overlapping pools of light. The count is then checked against a lumens target — light output per square foot — and the grid is tightened if the fixtures are too dim to reach it.
Use it for kitchens, living rooms, basements, bedrooms and offices. Brightness targets are approximate foot-candle levels for general ambient lighting; task areas such as countertops usually get extra under-cabinet or pendant lighting. Always check joist locations and insulation-contact (IC) ratings before cutting holes.
With the default inputs, the recessed lights needed is 16. Change any value above to recalculate instantly.
How to use the recessed lighting layout calculator
- 1Measure the room length, width and ceiling height.
- 2Choose a brightness target for how the room is used.
- 3Enter the lumen and wattage rating of the fixtures you plan to buy.
- 4Read the number of lights and the grid layout.
- 5Mark the positions on the ceiling, starting half a spacing from each wall.
Formula and method
The starting spacing S is half the ceiling height, a common rule for general recessed lighting that makes the light cones overlap at floor level. The number of fixtures along each wall is the room dimension divided by S, rounded to the nearest whole number (at least one), and the actual spacing is the dimension divided by that count. Placing the outer lights half a spacing from the walls centers the grid and keeps walls evenly lit.
The lumens check multiplies the floor area by the target foot-candles (1 fc ≈ 1 lumen per square foot) and divides by the fixture lumens. If the grid has fewer lights than that, columns or rows are added along the direction with the widest spacing until it does. The light level shown is total lumens ÷ area and ignores losses from trims, dirty lenses and dark finishes, so treat it as an upper estimate.
- H
- Ceiling height in feet
- L, W
- Room length and width in feet
- A
- Floor area in square feet
- fc
- Target light level in foot-candles
- lm
- Lumen output per fixture
Worked examples
16 × 14 ft living room, 8 ft ceiling
Half the 8 ft ceiling gives a 4 ft spacing: 16 ÷ 4 = 4 lights along the length and 14 ÷ 4 = 3.5, rounded to 4, across. That is a 4 × 4 grid at 4 ft by 3.5 ft, starting 2 ft and 1.75 ft from the walls. The brightness check (224 sq ft × 20 fc ÷ 650 lm = 7) is easily met.
12 × 10 ft kitchen with 9 ft ceiling and dim fixtures
The 4.5 ft rule spacing gives round(12 ÷ 4.5) = 3 by round(10 ÷ 4.5) = 2, only 6 lights. Reaching 30 fc over 120 sq ft at 500 lm needs 8 lights, so a column is added across the widest spacing, giving a 3 × 3 grid of 9.
20 × 15 ft basement, 7.5 ft ceiling, 800 lm lights
A 3.75 ft rule spacing gives round(20 ÷ 3.75) = 5 rows and round(15 ÷ 3.75) = 4 columns, so 20 lights spaced 4 ft by 3.75 ft. Brightness needs only 8 fixtures, so you could choose a wider spacing with brighter lights if you prefer fewer holes.
Frequently asked questions
How far apart should recessed lights be?+
A popular rule is to divide the ceiling height by two: about 4 ft apart on an 8 ft ceiling, 4.5 ft on 9 ft and 5 ft on 10 ft. Wider beam angles and brighter fixtures can be spaced farther apart.
How far should recessed lights be from the wall?+
For general lighting, place the first row about half the fixture spacing from the wall — roughly 2 to 3 ft. To wash a wall or highlight art, move them closer, around 1.5 to 2 ft away.
How many recessed lights do I need for a 12 × 12 room?+
With an 8 ft ceiling the 4 ft rule gives a 3 × 3 grid of 9 lights. For brightness alone, 144 sq ft at 20 foot-candles needs about 2,880 lumens, or five 650-lumen fixtures.
Should I use 4 inch or 6 inch recessed lights?+
6 in fixtures give broader, brighter light and suit general lighting in larger rooms; 4 in fixtures look sleeker, suit kitchens, task and accent lighting, and usually need closer spacing.
What is a foot-candle?+
A foot-candle is one lumen of light falling on one square foot. Living spaces are commonly lit to about 10–20 fc for ambient light, kitchens and offices to 30–50 fc for tasks.