Free lighting layout tool
Recessed Lighting Calculator
How many can lights your room needs, how far apart to space them, how far from the walls — plus a scaled layout diagram you can hand to your electrician.
1. Plan your layout
Two ways to use it: find the fixture count for your room, or check the spacing for a count you already have in mind.
Advanced: CU, light loss & LED efficacy
CU ≈ 0.6 is typical for residential downlights with a light ceiling (only ~60% of rated lumens usefully reach the work plane). LLF ≈ 0.8 reserves 20% for lumen depreciation and dirt over time.
2. Your layout
3. Lumens ⇔ LED watts
Quick conversion at typical LED efficacy. Adjust the efficacy for your exact fixtures.
4. Target light levels by room
Foot-candle targets from common IES-derived residential guidance. Dark walls and matte finishes absorb light — add 10–20% headroom.
| Room | Target (fc) | Range (fc) |
|---|
5. Worked example
12 × 10 ft kitchen, 8 ft ceiling, target 40 fc, 6-inch LED fixtures (1,100 lm each), CU 0.6, LLF 0.8:
Step 1 — light needed: 120 sq ft × 40 fc = 4,800 lumens.
Step 2 — usable lumens per fixture: 1,100 × 0.6 × 0.8 = 528 lm.
Step 3 — fixture count: 4,800 ÷ 528 = 9.09 → round up to 10 fixtures.
Step 4 — grid: 10 fixtures fit best as 5 columns × 2 rows.
Step 5 — spacing: 12 ÷ 5 = 2.4 ft along the length, 10 ÷ 2 = 5.0 ft along the width; wall offsets are half that: 1.2 ft and 2.5 ft.
Result: 10 fixtures deliver 11,000 lm ≈ 44.0 fc maintained (≈110 W total at 100 lm/W). Note the 5.0 ft row spacing exceeds the 4 ft rule-of-thumb for an 8 ft ceiling — the strict spacing-rule alternative is 9 fixtures in a 3 × 3 grid at 4.0 × 3.33 ft, delivering 39.6 fc.
Step 2 — usable lumens per fixture: 1,100 × 0.6 × 0.8 = 528 lm.
Step 3 — fixture count: 4,800 ÷ 528 = 9.09 → round up to 10 fixtures.
Step 4 — grid: 10 fixtures fit best as 5 columns × 2 rows.
Step 5 — spacing: 12 ÷ 5 = 2.4 ft along the length, 10 ÷ 2 = 5.0 ft along the width; wall offsets are half that: 1.2 ft and 2.5 ft.
Result: 10 fixtures deliver 11,000 lm ≈ 44.0 fc maintained (≈110 W total at 100 lm/W). Note the 5.0 ft row spacing exceeds the 4 ft rule-of-thumb for an 8 ft ceiling — the strict spacing-rule alternative is 9 fixtures in a 3 × 3 grid at 4.0 × 3.33 ft, delivering 39.6 fc.
6. Methodology
Fixture count (lumen method):
Spacing rule:
Wall offset:
Grid: the fewest fixtures ≥ N arranged in the most even rows × columns for the room's proportions; positions sit at half-spacing from each wall, so wall offset is always exactly half the spacing.
Achieved light:
N = ceil( area_ft² × target_fc ÷ (lumens_per_fixture × CU × LLF) )Spacing rule:
spacing ≈ ceiling_height ÷ 2 (typical range 3–6 ft).Wall offset:
wall_distance = spacing ÷ 2 per direction, so the first row washes the wall instead of leaving dark corners.Grid: the fewest fixtures ≥ N arranged in the most even rows × columns for the room's proportions; positions sit at half-spacing from each wall, so wall offset is always exactly half the spacing.
Achieved light:
fc = N × lumens × CU × LLF ÷ area_ft² (maintained, after losses).Scope boundary: this page is a layout planner — it tells you how many recessed downlights to install and exactly where to put them. For pure unit math (lumens ⇔ watts, lux ⇔ foot-candles, candela, nits), use our lighting unit converter instead.
Electrical safety: this tool plans light placement only. All wiring must follow local electrical code — when in doubt, have a licensed electrician do the installation, verify the circuit has capacity for the added load, and keep fixtures clear of insulation unless rated IC (insulation contact).
7. Frequently asked questions
How far apart should recessed lights be spaced?
The standard rule of thumb is spacing = half the ceiling height: an 8 ft ceiling means about 4 ft between fixtures, a 10 ft ceiling about 5 ft. In practice designers stay in the 3–6 ft range depending on the room — tighter (3–4 ft) for kitchens and task areas, wider (4–6 ft) for living rooms and hallways. This calculator also checks your layout against the rule and warns when a row ends up wider than the guideline.
How many recessed lights do I need in a room?
Use the lumen method: multiply the room area (sq ft) by the target foot-candles, then divide by each fixture's usable lumens (rated lumens × CU × LLF). Example: a 12 × 10 ft kitchen (120 sq ft) at 40 foot-candles needs 4,800 lumens; with 1,100-lumen 6-inch LEDs, CU 0.6 and LLF 0.8, each fixture delivers 528 usable lumens, so 4,800 ÷ 528 = 9.09 → 10 fixtures.
How far should recessed lights be from the wall?
Half the fixture spacing. With the common 4 ft spacing (8 ft ceiling), the first row sits about 2 ft from the wall — this washes the wall with light instead of leaving dark corners or harsh scallops. The layout diagram on this page marks the exact wall offset for each direction of your grid.
What foot-candle level does each room type need?
Common IES-derived residential targets: living room and bedroom 10–20 fc, dining room 10–30 fc, kitchen 30–50 fc ambient (70–80 fc over task areas like countertops), bathroom 70–80 fc at the vanity mirror, home office 30–50 fc, hallway 5–10 fc, media room about 10 fc. Dark walls and matte finishes absorb light, so add 10–20% headroom in low-reflectance rooms.
Should I choose 4-inch or 6-inch recessed lights?
6-inch trims are the general-purpose choice (typically around 1,100 lumens per LED fixture) and cover more area per fixture, so you need fewer of them. 4-inch trims (around 750 lumens) suit task and accent lighting, lower ceilings, and a more modern look — but expect a higher fixture count for the same light level. This calculator lets you toggle trim size and shows how the count changes.
Do recessed lights need to be on a dimmer?
Strongly recommended for living rooms, dining rooms, bedrooms, and media rooms, where you want bright light for cleaning and low light for relaxing — size the layout for the bright end and dim down from there. Only use fixtures labeled dimmable, and pair them with a compatible dimmer type (leading-edge/TRIAC or ELV, per the fixture manufacturer's list) to avoid flicker and buzz.
How many watts will my recessed lighting layout use?
Divide total lumens by LED efficacy (about 100 lumens per watt for modern LEDs). A 1,100-lumen 6-inch LED draws roughly 11 W, so the 10-fixture kitchen example on this page (11,000 lumens total) uses about 110 W with everything at full brightness — and far less in practice once dimmed.
How is this different from a lighting unit converter?
This is a layout planner: it answers how many downlights to install, where to put them, and how far apart — including a scaled grid diagram you can hand to an electrician. If you only need to convert between units (lumens ⇔ watts, lux ⇔ foot-candles, candela, nits), use our lighting unit converter instead.
Free tool by NRTechStudio