Lumens Calculator
This lumens calculator works out how much light a room needs. Enter the room length and width and the target light level in foot-candles, and the lumens calculator returns the total lumens, the number of bulbs or fixtures at your lumen rating, the approximate LED wattage, and the light level in lux.
Results
The Lumens Calculator is part of our Lighting Design collection. Browse more lighting design to size, convert, and check your work alongside this tool.
What the lumens calculator does
A foot-candle is one lumen spread over one square foot, so the light a room needs is its area times the target light level. The lumens calculator multiplies the two, divides by the output of the bulbs or fixtures you plan to use, and estimates the LED wattage from the efficacy. It also converts the light level to lux, the metric unit, at 10.76 lux per foot-candle.
Lumens per square foot formula
The calculator uses the definition of the foot-candle:
This is a quick rule; dark walls, high ceilings, and fixtures that send light upward lower the light that reaches the work surface, so add 10 to 30% in those rooms.
Lumens calculator example
A 12 × 15 ft kitchen at 40 foot-candles with 800 lumen LED bulbs at 90 lm/W:
The light level is about 431 lux. A 15 × 12 ft living room at 15 foot-candles needs only 2,700 lumens.
How to use the lumens calculator
Measure the room length and width in feet. Pick a target light level: about 10 to 20 foot-candles for living rooms and bedrooms, 30 to 50 for kitchens, bathrooms, offices, and garages, and 50 or more for workshops and detailed tasks. Enter the lumen rating of your bulbs or fixtures and the LED efficacy from the box, often 80 to 110 lumens per watt. Press Calculate.
Reading lumens per square foot results
The lumens figure is the total for even general lighting. Spread it over several fixtures rather than one bright one to avoid glare and dark corners, and add task lighting under cabinets, over desks, and at mirrors. Dimmers let one layout serve both bright work and relaxed evenings. If a room still looks dim after installation, the walls may be dark or the fixtures shielded; raise the target in the calculator and add light.
When to use a room lighting calculator
- Planning recessed lights in a kitchen
- Choosing LED bulbs for a living room
- Lighting a garage or workshop for detailed work
- Converting foot-candles to lumens or lux
- Checking a fixture count before an electrician quote
Common lumens calculator mistakes
- Shopping by watts. Compare lumens, not watts.
- One bright fixture. Spread light over several fixtures.
- Ignoring dark finishes. Add light for dark walls and high ceilings.
- No task lighting. Add light where you read, cook, or work.
Tips for room lighting calculator results
- Layer ambient, task, and accent lighting.
- Use dimmers for living and dining rooms.
- Choose high CRI LEDs where color matters.
Lumens to lux and lighting layout
Lux is lumens per square meter and the foot-candle is lumens per square foot, so one foot-candle equals 10.76 lux. Lighting designers use the lumen method, which adds two factors to this calculator: a coefficient of utilization for how much fixture light reaches the work plane, often 0.5 to 0.8 in a room with light walls, and a light loss factor for dirt and aging, often 0.8 to 0.9. Together they can mean you need 30 to 60% more lumens than the simple figure for the same light level, which is why the rule here is a starting point. For layout, a common spacing for recessed lights is about half the ceiling height to the wall and the full ceiling height between fixtures. Light colors on walls help, so plan paint together with lighting using the paint calculator.
LED lumens calculator and running cost
LEDs produce far more light per watt than incandescent or halogen bulbs, so the wattage for a room has fallen sharply. The 80 W kitchen in the example would have taken around 500 W of incandescent bulbs. Pick a color temperature of 2,700 to 3,000 K for warm living spaces and 4,000 to 5,000 K for workshops and garages, and check the color rendering index, 90 or more for kitchens and bathrooms. Work out the yearly cost of the lighting with the energy cost calculator.
Lumens per square foot by room
Common general lighting targets for homes and work spaces. Task areas may need more:
| Room | Foot-candles | Lux | Lumens for 150 sq ft |
|---|---|---|---|
| Living room | 10 to 20 | 108 to 215 | 1,500 to 3,000 |
| Bedroom | 10 to 20 | 108 to 215 | 1,500 to 3,000 |
| Dining room | 20 to 30 | 215 to 323 | 3,000 to 4,500 |
| Kitchen | 30 to 50 | 323 to 538 | 4,500 to 7,500 |
| Bathroom | 30 to 50 | 323 to 538 | 4,500 to 7,500 |
| Home office | 30 to 50 | 323 to 538 | 4,500 to 7,500 |
| Garage | 30 to 50 | 323 to 538 | 4,500 to 7,500 |
| Workshop | 50 to 100 | 538 to 1,076 | 7,500 to 15,000 |
Lumens Calculator FAQ
How many lumens do I need for a room?
Multiply the area in square feet by the target foot-candles. A 150 sq ft bedroom at 15 foot-candles needs about 2,250 lumens; a 180 sq ft kitchen at 40 needs 7,200.
How do I convert foot-candles to lux?
Multiply by 10.76. 40 foot-candles is about 430 lux.
How many watts is 800 lumens?
About 60 W for an old incandescent bulb, but only 8 to 10 W for an LED at 80 to 100 lumens per watt.
Does ceiling height matter?
Yes. Higher ceilings and dark walls lower the light that reaches the floor, so add 10 to 30% to the lumens.