How to use the recessed lighting calculator
- Enter the room length, width and ceiling height in feet.
- Set a target brightness in footcandles (lumens per square foot) for the room type.
- Enter the lumens of the fixture you plan to buy (printed on the box).
- Read the number of lights, rows, spacing and distance from the walls, and whether your fixtures are bright enough.
The spacing rule
Spacing between lights ≈ ceiling height ÷ 2
Lights per row = room length ÷ spacing (rounded) · Distance from wall = actual spacing ÷ 2
Spacing at about half the ceiling height lets the light cones from neighboring fixtures overlap at around head height, which gives even ambient light without dark spots. Placing the outer row at half the spacing from the wall keeps the light distribution even right to the edges and avoids harsh scallops on the walls.
How bright should a room be?
Lumens needed = room area (sq ft) × target footcandles
Typical residential targets, based on Illuminating Engineering Society (IES) guidance for ambient light:
- Living rooms and bedrooms: 10–20 footcandles
- Dining rooms: 20–30 fc (often plus a pendant over the table)
- Bathrooms: 20–30 fc ambient, more at the mirror
- Kitchens: 30–50 fc on work surfaces
- Home office / workshop: 40–50 fc
Typical LED recessed fixtures produce about 500–700 lumens (4-inch) or 650–1,100 lumens (6-inch). Dimmable fixtures let you install for the brightest need and turn them down for everyday use.
Worked example
A 14 × 12 ft living room with an 8 ft ceiling, target 20 fc, using 650-lumen 6-inch LEDs:
- Target spacing: 8 ÷ 2 = 4 ft
- Along 14 ft: 14 ÷ 4 = 3.5 → 4 lights per row, actual spacing 3.5 ft, first light 1.75 ft from the wall
- Along 12 ft: 12 ÷ 4 = 3 rows, spacing 4 ft, first row 2 ft from the wall
- Total: 3 × 4 = 12 lights
- Lumens needed: 168 sq ft × 20 fc = 3,360 lumens (280 per light)
- Your 12 × 650 lm = 7,800 lm ≈ 46 fc at full power — bright enough for a kitchen, so put them on a dimmer or choose 4-inch fixtures.
Layout tips
- Light the task, not just the room. In kitchens, place lights over the front edge of the counters (about 24–30 inches from the wall) so you do not work in your own shadow.
- Check joists first. Use a stud finder and shift the grid a few inches so no fixture lands on a joist; keep spacing as even as possible.
- Choose the color temperature once. 2700–3000 K feels warm for living spaces; 3500–4000 K suits kitchens and work areas. Do not mix them in one room.
- Use IC-rated fixtures where they touch insulation, and airtight (AT) fixtures for ceilings below an attic.
- Circuit load: a 15-amp, 120-volt circuit supplies 1,800 watts, and continuous loads are commonly kept to 80% (1,440 W) — that is over 100 typical 12 W LED fixtures. Have a licensed electrician handle new circuits where required by local code.
Frequently asked questions
How many recessed lights do I need?
Divide room length and width by half the ceiling height and multiply the results. A 12 × 12 ft room with an 8 ft ceiling needs a 3 × 3 grid of 9 lights.
How far apart should recessed lights be?
About half the ceiling height: 4 ft apart for 8 ft ceilings, 4.5 ft for 9 ft, 5 ft for 10 ft ceilings.
How far from the wall should recessed lights be?
About half the spacing between lights, typically 2 to 3 ft. In kitchens, center them over the front edge of the counter.
How many lumens do I need for a room?
Multiply the area by the target footcandles: about 10–20 for living rooms and bedrooms and 30–50 for kitchens.
Should I use 4-inch or 6-inch recessed lights?
6-inch fixtures give wider, brighter light for general lighting; 4-inch fixtures look cleaner and suit accent, task or tighter spacing.