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Recessed Lighting Calculator
Recessed (can or pot) lights are easiest to plan on paper. This calculator uses the lumen method to find how many fixtures give the brightness you want, arranges them in an even grid, and checks the result against the common spacing rule of half the ceiling height.
Enter your measurements
Enter your measurements and press Calculate to see quantities, a material breakdown and an optional cost estimate.
How the calculation works
- Fixture lumens needed = Target light level × Room area ÷ Usable light factor
- Lights = Fixture lumens needed ÷ Lumens per fixture, rounded up
- Spacing rule of thumb = Ceiling height ÷ 2
- Distance from walls = Spacing ÷ 2
A foot-candle is one lumen per square foot (about 10.76 lux). Multiplying the target level by the room area gives the lumens that must reach the room; dividing by the usable light factor allows for light absorbed by trims and walls and for LED ageing.
The light count is then arranged as an even grid that follows the room's proportions, so lights are spaced similarly in both directions.
Assumptions used
- Brightness levels are general planning values for ambient light, not code requirements. Kitchens, desks and vanities usually need extra task lighting.
- The usable light factor is an editable planning value. Dark walls, deep trims and narrow beam angles reduce it.
- Joists, ducts and existing wiring may force small layout shifts; keep spacing as even as possible.
Example calculation
A 16 × 12 ft living room with an 8 ft ceiling, medium brightness (20 fc), 650 lm fixtures and a 75% usable light factor.
- 1Area: 16 × 12 = 192 ft²
- 2Fixture lumens needed: 20 × 192 ÷ 0.75 = 5,120 lm
- 3Lights: 5,120 ÷ 650 = 7.9, so 8 lights
- 4Grid: 2 rows × 4 lights, spaced 4 ft × 6 ft, starting 2 ft and 3 ft from the walls
Result: 8 recessed lights in 2 rows of 4.
How to measure your project
- Measure the room wall to wall. For open-plan spaces, plan each zone (kitchen, dining, living) separately.
- Measure ceiling height from the floor. For sloped ceilings, use the average height and choose adjustable (gimbal) trims.
- Read the lumen output on the fixture box rather than relying on wattage.
Frequently asked questions
How far apart should recessed lights be?
A common rule of thumb is to divide the ceiling height by two: about 4 ft (1.2 m) apart for an 8 ft (2.4 m) ceiling. Keep lights roughly half that distance from the walls. Wider beam angles allow wider spacing.
How many lumens do I need for a room?
Multiply the room area by the light level you want. Living rooms and bedrooms are often planned around 10–20 foot-candles, kitchens and bathrooms 30–50, and work areas 50 or more. The calculator does this for you and allows for light losses.
Should I use 4 inch or 6 inch recessed lights?
Six-inch fixtures usually give more light per fixture, so you need fewer. Four-inch fixtures look neater and suit accent and task lighting but you need more of them. Enter the lumen rating of the model you plan to buy.
Can I install recessed lights myself?
Rules vary by location. Many areas require a licensed electrician or a permit for new circuits. Use fixtures rated for contact with insulation (IC-rated) where they touch insulation, and wet-rated fixtures in showers.
Results are estimates based on the measurements and assumptions you enter. Always confirm product specifications, local building codes and final quantities with your supplier or a qualified professional. See our disclaimer.