Lighting Calculator — Free Online Calculator
Calculate how many lumens and fixtures you need for any room based on size and use.
How to Use This Calculator
Enter room dimensions, select room type, and bulb brightness to find how many bulbs you need.
The Formula Explained
Total lumens = Room area × Lumens per square foot (varies by room type: 10-70 lm/sqft). Number of bulbs = Total lumens / Lumens per bulb.
Lighting Design Basics
Good lighting transforms a space. Poor lighting — too dim, too harsh, wrong color, or badly placed — makes even beautiful rooms feel uncomfortable and functional tasks difficult. Residential lighting design is part art and part science: the art is choosing fixtures and layouts that enhance the space aesthetically, while the science is ensuring adequate light levels for tasks and comfort. Modern LED lighting makes good design easier because the bulbs are efficient, long-lasting, and available in every imaginable color temperature and beam pattern.
The starting point for any lighting design is the task: what will people actually do in this space? Reading requires 30-50 footcandles at the book. Kitchen counter work requires 50-100 fc. Living room ambient viewing needs only 10-20 fc but benefits from dimming for mood. Hallways and stairs need 5-10 fc minimum for safety. Designing to these targets rather than generic "add more lights" approaches produces better results with fewer fixtures and lower energy use.
Worked Example: Kitchen Lighting Design
A 200 sq ft kitchen with L-shaped counters totaling 15 linear feet. Design for 50 fc general ambient and 75 fc on countertops.
General ambient: 200 sq ft × 50 fc = 10,000 lumens delivered. Accounting for fixture efficiency and room surfaces (CU of 0.7): 10,000 / 0.7 = 14,300 lumens needed at fixtures. Using 800-lumen LED bulbs (60W equivalent, 10W actual): 14,300 / 800 = 18 bulbs. That's too many for a kitchen. Use six 2,400-lumen LED recessed cans (18W each) = 14,400 lumens. Spacing: 4 feet apart in a 2x3 grid.
Task lighting on counters: 15 linear ft × 2 ft deep = 30 sq ft of work area at 75 fc = 2,250 lumens. Undercabinet LED strips at 250 lumens per linear foot × 15 ft = 3,750 lumens. Over-counter coverage achieved.
Total fixtures: 6 recessed cans (general) + undercabinet LED strips (task) + 1 decorative pendant over dining area (ambient accent). Total wattage: 6 × 18 + 150 (strips) + 40 (pendant) = 298W. LPD: 298 / 200 = 1.49 W/sq ft, exceeds California Title 24 residential kitchen limit of 1.1 W/sq ft. Reduce to high-efficiency LED cans at 12W each to comply.
Worked Example: Living Room Layered Lighting
A 300 sq ft living room with 9 ft ceilings. Design for layered lighting: ambient (general), task (reading), and accent (decor).
Ambient: 300 sq ft × 15 fc average = 4,500 lumens. Four 1,100-lumen LED recessed cans (4,400 lumens) or two ceiling fixtures at 2,200 lumens each. Dimmable for mood adjustment.
Task: reading chair and sofa areas each need about 400-600 lumens at 30 inches above the seat. Table lamps or floor lamps with 800-1,100 lumen bulbs provide this when turned on.
Accent: picture lights on art (50 lumens per picture, 2-3 pieces), wall washer fixtures for texture walls (100-200 lumens per wall), decorative pendant over coffee table or side table (250-500 lumens).
Total fixtures: 4 recessed + 2 table lamps + 2 picture lights + 1 decorative pendant = 9 light sources. This creates the layered effect that makes residential spaces feel welcoming rather than flat-lit like an office. The key: each layer can be independently dimmed or switched, letting occupants create different moods for different activities.
Lighting Design Mistakes
1. Single ceiling fixture for whole room. One central fixture creates unflattering shadows and poor distribution. Use multiple sources at different heights.
2. All same color temperature throughout the home. Warm for living/sleeping, neutral for bathrooms/hallways, cool for kitchens/workspaces. Consistency within a room, variety between rooms.
3. Ignoring dimming and control. Dimmers extend bulb life, save energy, and let you adjust for different activities. Smart controls (Lutron Caseta, Philips Hue) add scene presets and scheduling.
4. Underlighting task areas. Kitchen counters need 3-5x the general room lighting. Skimping here causes eye strain and accidents during food prep.
5. Ignoring color rendering (CRI). CRI 80 is minimum acceptable for residential; CRI 90+ shows food, skin, and art in true colors. Cheap LEDs often have CRI 70-75 which makes everything look wrong.
Lumens Needed by Room Type
Living Room (15-20 fc):
Small (150 sq ft): 2,250-3,000 lumens total.
Medium (200 sq ft): 3,000-4,000 lumens.
Large (300 sq ft): 4,500-6,000 lumens.
Kitchen (30-50 fc general + 75-100 fc task):
Small (100 sq ft): 3,000-5,000 general + 1,500-2,000 task.
Large (200 sq ft): 6,000-10,000 general + 3,000-4,000 task.
Bedroom (10-20 fc general + 40-80 fc reading):
Master (200 sq ft): 2,000-4,000 general + 800-1,600 reading.
Bathroom (30-50 fc):
Small (50 sq ft): 1,500-2,500 lumens plus vanity task light.
Dining Room (10-20 fc general + 30-40 fc table):
Medium (150 sq ft): 1,500-3,000 lumens, typically from a single chandelier or pendant.
Home Office (50-75 fc):
Standard (120 sq ft): 6,000-9,000 lumens for office work.
Design Standards and Codes
IES Recommended Practice (RP) series provides detailed recommendations for every type of space. California Title 24 and IECC set maximum lighting power density (LPD) limits for energy efficiency. ENERGY STAR certifies residential LED bulbs meeting quality and efficacy standards.
For professional lighting design, tools like Visual Lighting, AGi32, and Dialux model fixture photometrics, room surfaces, and output illumination levels at any point in 3D space. Residential projects can get by with simpler rules of thumb and manufacturer layout guides. Commercial projects almost always require calculated photometric layouts for energy code compliance.
Lighting design: lumens for room size and use category
Lighting design balances lumens per square foot (illuminance), light placement, glare control, and color quality. The calculator gives a starting-point lumen total for room area and use type, which you then divide into fixtures and bulbs. IES recommends 20-30 footcandles (215-325 lux) for general residential, 50+ for kitchens and work areas, 75-100 for serious task lighting.
The formula and what it does
Footcandles x sq-ft = lumens delivered to the work plane. Real fixtures deliver less than nameplate because of glare control, reflections, and depreciation. CU x LF (coefficient of utilization x light loss factor) typically 0.5-0.7, so divide target lumens by 0.6 for required fixture output.
Worked example
Scenario: 200 sq-ft kitchen, target 50 footcandles general + 100 footcandles task at counters.
General lighting: 200 x 50 / 0.6 = 16,667 lumens fixture output. 5 x 3,500 lm LED downlights (4-inch, 35 W each) at 175 W total. Task: under-cabinet LED strips at 600 lm/ft x 12 ft = 7,200 lm = 60 W. Total kitchen lighting: 235 W. Compares to old 8 x 60 W incandescent + 80 W fluorescent = 560 W. LED upgrade saves 325 W during use; better light quality and far more flexibility.
Common mistakes to avoid
undefinedFrequently asked questions
How many lumens do I need per square foot?
Residential general: 10-20 lm/sq-ft. Kitchen: 30-40. Bathroom vanity: 70-80. Office task: 50-75. Reading: 50-100 footcandles at the book. IES Lighting Handbook has detailed recommendations by use type.
How do I choose between 2700 K and 5000 K?
2700 K is warm (incandescent-like). 3000 K is slightly cooler. 4000 K is neutral white. 5000 K is daylight. Residential living areas: 2700-3000 K. Kitchen and bathroom: 3000-3500 K. Office task: 3500-4000 K. Outdoor security: 4000-5000 K.
What is CRI and what should I look for?
Color Rendering Index, how accurately colors appear vs sunlight reference. 80+ is acceptable, 90+ is excellent. Premium residential and food retail lighting: 90+ CRI essential.
How many recessed cans do I need?
Rule of thumb: divide ceiling height by 2 = spacing in feet. So 9 ft ceiling = cans every 4.5 ft. Refine with lumen calc above and adjust for room shape.
Should I use multiple light layers?
Yes. Good rooms have ambient (general), task (work surfaces), and accent (highlights). Single ceiling fixture is rarely enough for comfortable spaces.
How much wattage do I save going LED from CFL?
Roughly half. A 14 W CFL replaces a 60 W incandescent; a 9 W LED replaces the same 60 W. CFLs were never the final answer; LEDs dropped further.