Lumens needed = room area in square feet × footcandles for the room, because one footcandle is one lumen per square foot. A 15 by 12 ft living room at 15 lm per sq ft needs 2,700 lumens, which is four 800 lumen bulbs.
How the lumens calculator works
The Illuminating Engineering Society publishes recommended light levels for homes. The calculator takes the middle of each range and multiplies it by the room size. Then it divides by the lumens on the bulb package and rounds up, since a fractional bulb does not exist.
Lumens = area (sq ft) × footcandles; bulbs = lumens ÷ lumens per bulb, rounded up
Metric users read lux instead: one footcandle is 10.76 lux, and lumens = lux × area in m².
Lumens per square foot by room type
| Room | IES footcandles | Calculator target |
|---|---|---|
| Living room | 10 to 20 | 15 |
| Dining room | 10 to 20 | 15 |
| Bedroom | 20 to 50 | 35 |
| Kitchen, general | 20 to 50 | 35 |
| Kitchen, cooking and prep | 50 to 100 | 75 |
| Bathroom | 20 to 50 | 35 |
| Hallway | 5 to 10 | 7.5 |
| Office, difficult reading | 50 to 100 | 75 |
| Workshop or garage | 20 to 75 | 47.5 |
| Laundry | 20 to 100 | 60 |
The table follows the IES ranges as published by Super Bright LEDs; the target is the midpoint. Older eyes and dark paint or floors call for the top of the range.
Worked example: living room, 15 by 12 ft
- Area: 15 ft × 12 ft = 180 sq ft
- Lumens: 180 sq ft × 15 lm per sq ft = 2,700 lm
- Bulbs: 2,700 ÷ 800 lm = 3.4, rounded up to 4 bulbs, which deliver 3,200 lm
Swap the bulb for 450 lumens and the same room needs 6 bulbs; with 1,600 lumen bulbs it takes 2.
Lumens by room size
Room size decides everything else. A 10 by 10 ft bedroom (100 sq ft) at 35 lm per sq ft needs 3,500 lm. A 12 by 14 ft kitchen (168 sq ft) at 35 lm per sq ft needs 5,880 lm, and at the cooking target of 75 it needs 12,600 lm. A 5 by 8 ft hallway (40 sq ft) at 7.5 lm per sq ft needs only 300 lm. Enter the area directly with "I know the area" when the room is not a rectangle, or find it first with the room square footage calculator.
Lumens to bulb watts
ENERGY STAR lists the light a bulb must give to replace an old incandescent: 40 W is 450 lm, 60 W is 800 lm, 75 W is 1,100 lm, 100 W is 1,600 lm and 150 W is 2,600 lm. The Department of Energy's purchasing guide shows LEDs making the same light for far less power, for example 5.9 to 10.5 W for 800 lm, and the FTC quotes about 9 W. Buy by lumens and compare the watts only to see the running cost.
What to do next
- Turn the total into can lights with the recessed lighting calculator, which also checks spacing by ceiling height.
- See what an LED swap saves with the LED savings calculator.
- Price the running cost with the electricity cost calculator or the kWh calculator.
- Pick a fixture for the dining room with the chandelier size calculator.
- Browse the electrical calculators.