Project Parameters
Length of the room in feet.
Width of the room in feet.
Instant Estimate
Suggested Downlights (800 lm each)
Provides balanced ambient illumination across the ceiling plane.
Total Equivalent LED Wattage
Modern LED efficiency (~80–90 lumens/watt).
Recommended Illumination
Standard IES (Illuminating Engineering Society) guideline.
Room Surface Area
See it before you build
Upload a photo of your home and preview your project in 30+ styles with AI. Free designs, no credit card.
Guide
How to calculate lumens and light fixtures for any room
Lighting designers measure brightness in lumens (light output) and foot-candles (lumens per square foot hitting a surface). A task-heavy kitchen requires 40 foot-candles, while a relaxing bedroom only needs 15.
Find Room Area
Multiply room length by width in feet to determine square footage.
Multiply by Foot-Candles
1 Foot-Candle = 1 Lumen per square foot. Multiply room square feet by the room's recommended foot-candle rating.
Divide into Fixture Quantities
Divide total lumens by the lumen rating of your chosen light bulbs or recessed LED cans (typically 650 to 800 lumens per can).
Mathematics
Formulas used
Total Lumens
Room Area (sq ft) × Target Foot-CandlesTotal light energy needed for proper ambient vision.
Number of Downlights
Ceil(Total Lumens / Lumens per Fixture)Even distribution of ceiling recessed downlights.
Answers & FAQ
Frequently asked questions
How many lumens do I need for a 12x12 bedroom?▼
A 144 sq ft bedroom needs about 15 foot-candles = ~2,160 lumens total (equivalent to three 800-lumen fixtures or LED bulbs).
How far apart should recessed lights be spaced?▼
The general rule of thumb is to divide ceiling height by 2. For an 8 ft ceiling, space recessed lights 4 feet apart. For a 10 ft ceiling, space them 5 feet apart.
Related calculators
Interior Paint Calculator
Calculate wall and ceiling paint gallons, trim coverage, primer, and material cost.
Drywall Sheet Calculator
Calculate drywall sheets (4x8 and 4x12), screws, joint compound mud, and tape.
Color Palette Generator
Generate harmonious 60-30-10 color schemes, complementary, analogous, triad, and hex values.