Room Lumens Calculator

The short answer

Multiply the room’s floor area in square feet by the light level its type needs, in footcandles: 10 to 20 footcandles for a living room, 10 to 20 footcandles for a bedroom, 30 to 40 footcandles for a kitchen and 70 to 80 footcandles for a bathroom. One footcandle is one lumen per square foot, so a 12 by 15 ft living room needs about 1,800 to 3,600 lumens of general light. With bulbs of 800 lumens, the old 60 W kind, that’s 3 to 4 bulbs.

How to measure

1. Measure the floor wall to wall in both directions. For an L-shaped room, work out each part separately and add them.
2. Measure the ceiling height from the floor to the ceiling.
3. Look at the walls: pale and mid tones count as light or medium; deep colors and dark wood paneling count as dark.
4. Check the bulbs you plan to use: the box gives their brightness in lumens.

How to use the calculator

1. Pick the room type and enter its width, length and ceiling height.
2. Choose the walls and the bulbs you’d like to count in.
3. Read the result: the lumens of general light the room needs, how many of your bulbs add up to it and how many it takes with the other common sizes.
4. Save or share it. Copy link keeps your numbers in the address.

How we calculate

The light levels below are a starting point for the room’s general light. How bright you like a room decides the rest.

• Light level: the footcandles for each room type: living room 10 to 20 footcandles, bedroom 10 to 20 footcandles, kitchen 30 to 40 footcandles, dining room 30 to 40 footcandles, bathroom 70 to 80 footcandles, home office 60 to 80 footcandles and hallway or entry 5 to 10 footcandles. Each is a range, so the result is one too.
• Lumens: one footcandle is one lumen spread over one square foot, so the floor area times the footcandles gives the lumens. In metric, one footcandle is about 10.76 lux.
• More light: the levels assume a ceiling of about 8 ft and light or medium walls. With a ceiling of 10 ft or higher, or with dark walls, we add 10 to 20 percent, once, even when both apply. To see how much light a wall color reflects, the room color palette generator shows its LRV.
• Bulbs: the fewest bulbs that reach the low end of the range, up to the most that stay within its high end, counting every bulb in the room’s ceiling lights and lamps.
• A simplification: the formula doesn’t account for the direction a fixture throws its light, how much the walls and ceiling reflect or your own taste, so a room may need a little more or less.

Worked examples

Worked example

A 12 × 15 ft living room

What we know

• Room: living room, 12 × 15 ft
• Ceiling: 9 ft
• Walls: light or medium
• Bulbs: 800 lumens (60 W equivalent)

How it works out

1. Floor area: 12 × 15 ft = 180 sq ft.
2. Living room: 10 to 20 footcandles, one lumen per square foot each: 180 × 10 to 180 × 20 = 1,800 to 3,600 lumens.
3. Bulbs of 800 lumens: 3 give 2,400 lumens and 4 give 3,200, both in the range.

A 12 × 15 ft living room (180 sq ft) needs about 1,800 to 3,600 lumens of general light, 10 to 20 footcandles. That's 3 to 4 bulbs of 800 lumens (60 W equivalent), counting every bulb in the room's ceiling lights and lamps.

Worked example

A 10 × 12 ft kitchen with an 8 ft ceiling

What we know

• Room: kitchen, 10 × 12 ft
• Ceiling: 8 ft
• Walls: light or medium
• Bulbs: 800 lumens (60 W equivalent)

How it works out

1. Floor area: 10 × 12 ft = 120 sq ft.
2. Kitchen: 30 to 40 footcandles, one lumen per square foot each: 120 × 30 to 120 × 40 = 3,600 to 4,800 lumens.
3. Bulbs of 800 lumens: 5 give 4,000 lumens and 6 give 4,800, both in the range.

A 10 × 12 ft kitchen (120 sq ft) needs about 3,600 to 4,800 lumens of general light, 30 to 40 footcandles. That's 5 to 6 bulbs of 800 lumens (60 W equivalent), counting every bulb in the room's ceiling lights and lamps.

Worked example

A 12 × 12 ft bedroom with a 10 ft ceiling

What we know

• Room: bedroom, 12 × 12 ft
• Ceiling: 10 ft
• Walls: light or medium
• Bulbs: 1,100 lumens (75 W equivalent)

How it works out

1. Floor area: 12 × 12 ft = 144 sq ft.
2. Bedroom: 10 to 20 footcandles, one lumen per square foot each: 144 × 10 to 144 × 20 = 1,440 to 2,880 lumens.
3. Add 10 to 20 percent for the 10 ft ceiling: 1,590 to 3,450 lumens.
4. Bulbs of 1,100 lumens: 2 give 2,200 lumens and 3 give 3,300, both in the range.

A 12 × 12 ft bedroom (144 sq ft) needs about 1,590 to 3,450 lumens of general light, 10 to 20 footcandles. It includes 10 to 20 percent more for the 10 ft ceiling. That's 2 to 3 bulbs of 1,100 lumens (75 W equivalent), counting every bulb in the room's ceiling lights and lamps.

Lumens by room

The lumens of general light each room type needs, for two common room sizes, with a ceiling under 10 ft and light or medium walls.

Lumens and watts

Bulbs are sold by lumens now, but the box usually names the old incandescent bulb it replaces.

Before you buy

General light is only part of a room’s lighting. Where you read, cook or get ready, add light at that spot: a lamp beside the chair, lights under the kitchen cabinets, light at the bathroom mirror. Those come on top of the room’s total. In a bathroom, the bathroom fan CFM calculator takes the same room size to the exhaust fan.