Recessed lighting calculator
A free recessed lighting calculator: fixture count by the spacing rule and the lumen method, even spacing from the walls, and a top-view layout drawn to scale. US practice only.
Room and fixtures
Living room: 10–20 fc is a commonly cited guidance range for general lighting, not a code requirement. The lumen default (650 lm for a 4 in fixture) is a typical LED value; the fixture's data sheet governs.
Layout (top view, to scale)
"Open as lighting plan" saves the layout as a new board in this browser's workspace and opens it; nothing is uploaded.
How to calculate recessed lighting
A recessed lighting layout sets how many ceiling fixtures a room needs and where they go, so that the light is even across the floor and bright enough for the room's use. Two quick methods are in common use, and the calculator runs both.
The spacing rule works from the ceiling height: fixtures about half the ceiling height apart, and about half that spacing from the walls. It gives even coverage but says nothing about brightness. The lumen method works from the light level wanted: the room's floor area times a target in foot-candles gives the lumens needed, and dividing by the lumens of one fixture gives the count.
Because one method controls evenness and the other brightness, the calculator recommends the larger of the two counts and then lays that number out on an even grid, with every fixture centered in an equal share of the ceiling.
The spacing rule, with a worked example
The rule of thumb is spacing ≈ ceiling height ÷ 2. The number of fixtures along each wall is that wall's length divided by the spacing, rounded to a whole fixture; the actual spacing is then the wall length divided by the count, and the first and last fixtures sit half a spacing from the walls.
For a 12 × 14 ft room with an 8 ft ceiling, the target spacing is 8 ÷ 2 = 4 ft. Along the 14 ft wall, 14 ÷ 4 = 3.5, which rounds to 4 fixtures at 3 ft 6 in apart and 1 ft 9 in from each end wall. Along the 12 ft wall, 12 ÷ 4 = 3 fixtures at 4 ft apart and 2 ft from each side wall.
The result is a 3 × 4 grid of 12 fixtures. Each fixture serves a 3 ft 6 in × 4 ft patch of ceiling, and the half spacing at the walls keeps the room's edges as bright as its middle.
The lumen method, with a worked example
The lumen method in its simple form is: required lumens = floor area (sq ft) × target foot-candles; fixtures = required lumens ÷ lumens per fixture, rounded up. One foot-candle is one lumen per square foot.
For the same 12 × 14 ft room used as a kitchen, the area is 168 sq ft. At 30 foot-candles, a commonly cited figure for general kitchen lighting, the room needs 168 × 30 = 5,040 lumens. With 4 in fixtures of 650 lumens each, 5,040 ÷ 650 = 7.75, rounded up to 8 fixtures; with 6 in fixtures of 900 lumens, 6.
Here the spacing rule's 12 fixtures exceed the lumen method's 8, so the spacing rule governs and the light level comes out above the target. The reverse happens in brighter rooms: as a workshop at 50 foot-candles, the same room needs 8,400 lumens, or 13 fixtures of 650 lumens, more than the spacing rule's 12. The calculator then lays out the most even grid that holds them: 3 rows of 5, 15 fixtures.
The foot-candle presets are commonly cited guidance ranges for general lighting, not code requirements; each one can be changed. A full lumen-method calculation also applies a coefficient of utilization and a light loss factor, which reduce the light reaching the floor, so the simple version tends to overstate the delivered level.
Layout tips
Sloped and vaulted ceilings. On a slope, the spacing is set from the average ceiling height, and fixtures are chosen with a sloped-ceiling trim or an adjustable gimbal so the light points down rather than along the slope. Rows run parallel to the ridge so that each row sits at one height.
Task lighting over counters. Kitchen counters and islands get fixtures centered over the front edge of the counter, typically about 12 to 18 inches out from the upper cabinets, so a person standing at the counter does not shade the work surface. These are laid out in addition to the room's general grid.
Dimmers. A dimmer lets one layout serve several uses: full output for cleaning and tasks, lower levels for evening use. LED fixtures need a dimmer listed as compatible with them, and the dimmer's rating limits how many fixtures one control can carry.
Circuits and controls. Grouping fixtures into zones, such as perimeter, center and task, on separate switches or dimmers gives more control than a single switch. The total fixture wattage sets the load on each lighting circuit; the breaker size and voltage drop calculators check that circuit.
Recessed lighting vs other fixtures
Recessed fixtures sit flush with the ceiling and light the floor in a cone, so a room needs several of them for even coverage. A single surface-mounted or pendant fixture spreads light more widely from one point and is simpler to wire, but it leaves corners darker and hangs in the sightline.
Track and wall-wash fixtures aim light at walls, art or shelving; they complement a recessed grid rather than replace it. Many rooms use recessed fixtures for general light and pendants or under-cabinet strips for tasks.
Slim LED wafer fixtures install without a housing in many ceilings and are lighter to retrofit than traditional cans. In ceilings with insulation, NEC 410.116 requires fixtures in contact with insulation to be Type IC; fixtures over a tub or shower must be listed for damp or wet locations under 410.10(D).
Limitations
This calculator is not a photometric design. It does not model a fixture's beam angle, distribution, the room's surface reflectances or the light lost to dirt and aging, and it assumes a flat ceiling and an open, rectangular floor.
Fixture lumen output, beam spread and spacing criteria come from the manufacturer's data sheet or IES photometric file, which take precedence over the defaults used here. For rooms where the light level matters, such as offices, workshops and commercial spaces, a lighting designer's point-by-point calculation is the reliable method.
The locally adopted energy code, such as the IECC or California's Title 24, Part 6, can limit lighting power and require high-efficacy sources, dimming or occupancy controls. The NEC and the authority having jurisdiction set the wiring and fixture requirements; this page does not cover them in full.
Frequently asked questions
How far apart should recessed lights be?
A common rule of thumb is about half the ceiling height: roughly 4 ft apart on an 8 ft ceiling and 5 ft apart on a 10 ft ceiling, with the outer fixtures about half that distance from the walls. The fixture's data sheet may give its own spacing criterion, which takes precedence.
How many recessed lights does a 12 × 12 room need?
With an 8 ft ceiling the spacing rule gives a 3 × 3 grid of 9 fixtures, 4 ft apart and 2 ft from the walls. The lumen method may call for more in a brightly lit room such as a kitchen or office, or fewer in a bedroom; the calculator compares both.
How far from the wall should recessed lights be?
About half the spacing between fixtures, which on an 8 ft ceiling is about 2 ft. Fixtures much closer to the wall throw bright scallops of light down the wall; fixtures much farther away leave the room's edges darker.
Should 4 inch or 6 inch recessed lights be used?
Six-inch fixtures usually give more light each, so fewer are needed for the same light level, and they suit general lighting in larger rooms. Four-inch fixtures look less prominent and suit smaller rooms, accent and task lighting, but need closer spacing or more fixtures for the same brightness.
How many lumens does a room need?
Floor area times the target foot-candles. A 150 sq ft bedroom at 10 foot-candles needs about 1,500 lumens; a 150 sq ft kitchen at 30 foot-candles needs about 4,500. The targets are guidance ranges that vary with the room's use and the occupants, not code requirements.