About the Room Lighting Lumens Calculator
This room lighting calculator works out how many lumens you need to light a room well, and how many bulbs or fixtures that takes. Enter the room dimensions, pick the type of room, and enter the lumens of the bulb you plan to use; it returns the total lumens, the bulb count, and roughly how many LED watts that is.
Light levels are expressed in foot-candles (lumens per square foot) or lux (lumens per square metre). Rooms used for detailed tasks such as kitchens, bathrooms and workshops need several times more light than bedrooms or living rooms. The presets use the midpoint of commonly recommended residential ranges, and you can enter your own target instead.
The result is the ambient light that should reach the floor and work surfaces. Dark walls, very high ceilings and shaded or deep fixtures absorb light, so add 10–25% in those rooms, and use dimmers so a bright design can still feel relaxed in the evening.
With the default inputs, the total lumens needed is 2,700 lm. Change any value above to recalculate instantly.
How to use the room lighting lumens calculator
- 1Choose feet or metres and enter the room length and width.
- 2Pick the room type, or choose Custom and enter your own target.
- 3Enter the lumens printed on the bulb or fixture box.
- 4Read the total lumens and the number of bulbs needed.
- 5Add 10–25% for dark finishes or ceilings above 9 ft.
Formula and method
A foot-candle is one lumen spread over one square foot, and a lux is one lumen over one square metre, so the lumens a room needs equal its floor area multiplied by the target illuminance in the matching unit. One foot-candle equals 10.764 lux.
The bulb count divides the total by the output of one bulb and rounds up. LED watts are lumens divided by the efficacy in lumens per watt (around 80–110 lm/W for typical household LEDs). The incandescent equivalent uses the familiar 800 lm ≈ 60 W rule. This is a simple lumen method that ignores light loss from dark surfaces, dirty fixtures and tall ceilings, so increase the target in those cases.
- fc
- Foot-candles: lumens per square foot
- lux
- Lumens per square metre (1 fc = 10.764 lux)
- lm/W
- Luminous efficacy of the bulb
Worked examples
15 × 12 ft living room with 800 lm bulbs
The room is 180 sq ft. At 15 foot-candles it needs 180 × 15 = 2,700 lumens. That is 3.4 bulbs of 800 lm, so four, using about 30 W of LED at 90 lm/W.
12 × 10 ft kitchen with 1,100 lm fixtures
A 120 sq ft kitchen at 35 foot-candles needs 4,200 lumens. Fixtures giving 1,100 lm each cover that with four (3.8 rounded up), about 47 W of LED.
4 × 3.5 m bedroom in metric
15 foot-candles is about 161 lux. A 14 m² bedroom therefore needs 14 × 161.46 ≈ 2,260 lumens, which three 800 lm bulbs provide.
Frequently asked questions
How many lumens do I need per square foot?+
Common residential guidance is about 10–20 lumens per square foot for living rooms and bedrooms, 30–40 for kitchens and dining rooms, and 70–80 for bathrooms and other task-heavy spaces. Hallways can get by with 5–10.
How many lumens is a 60 watt bulb?+
A traditional 60 W incandescent bulb produces about 800 lumens. A 75 W bulb is about 1,100 lumens and a 100 W bulb about 1,600 lumens. LED replacements give the same light at roughly 8–15 W.
What is the difference between lumens and lux?+
Lumens measure the total light a bulb emits. Lux measures how much of that light lands on a surface, in lumens per square metre. Foot-candles are the same idea per square foot; 1 foot-candle equals about 10.76 lux.
Do high ceilings need more lumens?+
Yes. Light spreads and weakens with distance, so a room with 10–12 ft ceilings needs more output from ceiling fixtures to reach the same level at floor and counter height. Adding 10–25% or using more fixtures is a common adjustment.
How many recessed lights do I need?+
Divide the total lumens by the output of one recessed light. Six-inch LED downlights often give 650–1,000 lm. Spacing matters too; the recessed lighting calculator lays out a grid based on ceiling height.