Recessed Lighting Calculator

How many recessed lights do I need? Enter room size, ceiling height, and room type, get fixture count, spacing guide, wall offset, and a layout preview.

Foot-candles (fc) = lumens per square foot.

Typical LED recessed: 700–1,000 lm. Check your fixture spec sheet.

Standard rule: 0.8 × ceiling height for center-to-center spacing.

Distance from wall to first fixture center. Typical: 2–3 ft.

Layout Preview

Dots show approximate fixture centers. Grid scales to your room dimensions.

Recessed Lighting Calculator — Fixture Count, Spacing & Layout Guide

This calculator estimates how many recessed lights you need based on room size, ceiling height, target brightness (foot-candles), and lumens per fixture. It also generates a rows × columns grid layout and suggests spacing and wall offset as a starting point for your installation plan.

Recessed Lights Needed by Room Size

RoomAreaLiving room (15 fc)Kitchen ambient (40 fc)Suggested grid
10×10 ft100 ft²2 fixtures5 fixtures2×2 or 2×3
12×12 ft144 ft²3 fixtures7 fixtures2×2 or 3×2
15×12 ft180 ft²3 fixtures8 fixtures3×2 or 3×3
20×15 ft300 ft²5 fixtures14 fixtures4×3 or 4×4
24×18 ft432 ft²8 fixtures20 fixtures4×4 or 5×4

Based on 900 lm/fixture, 9 ft ceiling. Grid is based on 0.8 × ceiling height spacing rule. 12×12 ft highlighted as most common bedroom/living room size.

Target Foot-Candle Levels by Room Type

Room typeTarget foot-candlesNotes
Hallway5–10 fcNavigation only, low brightness acceptable
Bedroom / living room10–20 fcAmbient, use dimmers for flexibility
Bathroom30–50 fcHigher near mirror/vanity area
Kitchen (ambient)30–50 fcGeneral room lighting
Kitchen (task / countertop)70–100 fcOver counters, island, prep areas
Office / study30–50 fcReduces eye strain for reading and screens

How the Spacing Rule Works

The standard recessed lighting spacing rule: center-to-center spacing = 0.8 × ceiling height. For a 9 ft ceiling: 9 × 0.8 = 7.2 ft between fixtures. For an 8 ft ceiling: 6.4 ft. The first row should sit approximately half the spacing distance from the wall — about 3–4 ft from walls for a 9 ft ceiling.

The calculator grows the grid automatically until it can accommodate all fixtures required by the lumens calculation. The result is a practical starting grid, always adjust for joists, vents, structural elements, and any specific lighting zones.

Frequently Asked Questions

Multiply room area by target foot-candles, divide by lumens per fixture, and round up. For a 15×12 ft living room (180 sq ft) at 15 fc with 900-lumen fixtures: 180 × 15 = 2,700 ÷ 900 = 3 fixtures minimum. In practice, spacing rules often suggest 6–8 for even coverage. Enter your room above for an instant layout.
Standard rule: ceiling height × 0.8 for center-to-center spacing. For a 9 ft ceiling: 7.2 ft. For an 8 ft ceiling: 6.4 ft. The first row goes roughly half that distance from the wall — about 3–4 ft from walls for a 9 ft ceiling. Adjust for joists, beams, and vent locations.
A 12×12 ft room (144 sq ft) needs approximately 3 fixtures by the lumens formula for a living room (15 fc, 900 lm/fixture), but spacing rules typically suggest a 2×2 or 3×2 grid (4–6 fixtures) for even coverage without dark corners. For a kitchen at 40 fc, the same room needs 7 fixtures — a 3×2 or 3×3 grid.
For general lighting: 2–3 ft from the wall as a starting point. The calculator defaults to half the grid spacing. For wall-wash lighting (highlighting artwork or accent walls): 12–18 inches from the wall, depending on beam angle. Check your fixture's beam angle spec — a narrow beam placed too close will create scalloping on the wall.
Most LED recessed fixtures provide 700–1,000 lumens. 900 lumens is a good planning default. For kitchens and task areas, look for 1,200–1,500 lm fixtures. Always check the actual lumen output on the product spec sheet — wattage is not a reliable guide for LED brightness.
Foot-candles (fc) measure how much light falls on a surface, lumens per square foot. Typical targets: hallways 5–10 fc, bedrooms/living rooms 10–20 fc, bathrooms 30–50 fc, kitchens ambient 30–50 fc, kitchen task areas 70–100 fc. The calculator presets these by room type automatically.

Accuracy & Review

Reviewed by: Sonia Cho

Sonia reviews our lighting and electrical tools, validating spacing guidance, fixture density assumptions, and calculation logic for practical planning use.

Last updated:

See: Methodology · Data Sources · Review Board

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Disclaimer: Results are general planning estimates only. Actual fixture counts depend on specific fixture beam angles, ceiling height, room shape, obstructions, and local electrical code. Always consult a licensed electrician for final system design.

See Methodology and Data Sources for details.