How many recessed lights do you need? The answer depends on your room size, ceiling height, and fixture output — but most rooms follow a simple spacing rule that takes 60 seconds to apply.
The quick method: how many recessed lights do you need?
There are two ways to calculate the number of recessed lights. The spacing rule gives you a layout. The lumen method checks that the layout delivers enough light. Use both — they take about 60 seconds with the calculator above.
Rule 1 — spacing from walls and each other
Rule 2 — how many lumens does the room need?
Each room type has a recommended illuminance (brightness) level. Multiply the floor area by the target lumens per square foot to get the total lumens needed, then divide by the output of each fixture.
| Room type | Target (lm/sq ft) | 12×15 ft room | Fixtures at 800lm each |
|---|---|---|---|
| Bedroom | 10–20 | 1,800–3,600 lm | 3–5 fixtures |
| Living room | 10–20 | 1,800–3,600 lm | 3–5 fixtures |
| Kitchen (general) | 30–40 | 5,400–7,200 lm | 7–9 fixtures |
| Kitchen (task/island) | 50–75 | Add dedicated task lights | — |
| Home office | 30–50 | 5,400–9,000 lm | 7–12 fixtures |
| Bathroom | 50–75 | Use vanity + recessed | 2–4 + vanity bar |
| Hallway | 5–10 | Single-row spacing | 1 per 6–8 linear ft |
Room-by-room quick reference
| Room size | Ceiling height | Fixtures needed | Spacing |
|---|---|---|---|
| 8×10 ft (80 sq ft) | 8 ft | 3–4 | 4 ft grid |
| 10×12 ft (120 sq ft) | 8 ft | 4–6 | 4 ft grid |
| 12×15 ft (180 sq ft) | 9 ft | 6–8 | 4–5 ft grid |
| 14×18 ft (252 sq ft) | 9 ft | 8–12 | 4–5 ft grid |
| 16×20 ft (320 sq ft) | 10 ft | 10–14 | 5–6 ft grid |
| 20×20 ft (400 sq ft) | 10 ft | 12–16 | 5–6 ft grid |
What size recessed light should I use?
The size of the fixture (4 inch vs 6 inch) affects the beam spread and how much of the ceiling it illuminates — not the total brightness of the room. Choose based on ceiling height:
| Fixture size | Best ceiling height | Beam spread | Common use |
|---|---|---|---|
| 4 inch | Up to 9 ft | Narrow — good for accents | Hallways, accents, low ceilings |
| 6 inch | 8–12 ft | Wider — best for general lighting | Living rooms, bedrooms, kitchens |
| 8 inch | 12 ft+ | Very wide — for high ceilings | Vaulted ceilings, great rooms |
Common mistakes to avoid
Too few lights near walls. Most people centre their grid and end up with dark corners. Place the first row 2 ft from the wall, not 4 ft.
Installing on a single switch. Split recessed lights across at least two circuits so you can dim half the room for movie watching or evening ambience.
Wrong colour temperature (CCT). Bedrooms and living rooms look best at 2700K–3000K (warm white). Kitchens and home offices suit 3000K–4000K. Mixing CCTs on the same ceiling looks unprofessional.
Ignoring insulation contact (IC) rating. If your ceiling has insulation above it, you must use IC-rated fixtures. Non-IC lights create a fire risk when covered by insulation.
Frequently asked questions
Calculate yours in 60 seconds
Enter your room dimensions, ceiling height, and preferred lux level — the calculator handles the rest and shows a suggested grid layout.
Open the Recessed Lighting Layout Calculator →