How many lumens do I need?
Type the room size and pick a light level. The lumens calculator multiplies the area by the light level and counts the bulbs needed at the brightness you choose.
- Lumens needed
- 4,320
You need about 4,320 lumens, or 6 bulbs.
- Bulbs
- 6
- Light level (foot-candles)
- 30
- Light level (lux)
- 322.9
- Area (ft²)
- 144
- Area (m²)
- 13.38
Lumens needed: 4,320. You need about 4,320 lumens, or 6 bulbs.
How to calculate
Works out the lumens a room or work area needs from its size and a target light level in foot-candles or lux, and how many bulbs of a chosen brightness give it.
Example with the default inputs (Size in feet, Length 12, Width 12, Light level Offices, first aid stations (30 fc, OSHA), Bulb brightness 800 lumens (60 W incandescent)): You need about 4,320 lumens, or 6 bulbs.
Method: lumens = area × light level (ft² × foot-candles, or m² × lux); bulbs = lumens ÷ lumens per bulb, rounded up.
- All the light from the bulbs reaches the work surface. Real rooms lose some to walls, shades and dirt, so a lighting designer adds more.
- The OSHA levels are legal minimums for construction sites and the offices on them, not comfort levels for a home.
- 1 foot-candle = 1 lumen per square foot = 10.7639 lux (1 ft = 0.3048 m exactly).
Worked examples
Each example is checked against the calculator on every build.
- Size in feet, Length 12, Width 12, Light level Offices, first aid stations (30 fc, OSHA), Bulb brightness 800 lumens (60 W incandescent) gives Lumens needed 4,320, Bulbs 6, Light level (foot-candles) 30, Light level (lux) 322.9, Area (ft²) 144.Source: OSHA 29 CFR 1926.56, Illumination, Table D-3 (minimum foot-candles), https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.56; NIST SP 811, Appendix B.9 (footcandle and lumen per square foot to lux: × 10.76391; 1 ft = 0.3048 m), https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9; US DOE FEMP, Purchasing Energy-Efficient Light Bulbs, Table 2 (450, 800, 1,100 and 1,600 lumens for 40, 60, 75 and 100 W bulbs), https://www.energy.gov/cmei/femp/purchasing-energy-efficient-light-bulbs
- Size in meters, Length 4, Width 3, Light level Type my own, Target light level 300, Light level in lux, Bulb brightness 1,100 lumens (75 W incandescent) gives Lumens needed 3,600, Bulbs 4, Area (m²) 12, Light level (foot-candles) 27.9.Source: NIST SP 811, Appendix B.9 (footcandle and lumen per square foot to lux: × 10.76391; 1 ft = 0.3048 m), https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9; US DOE FEMP, Purchasing Energy-Efficient Light Bulbs, Table 2 (450, 800, 1,100 and 1,600 lumens for 40, 60, 75 and 100 W bulbs), https://www.energy.gov/cmei/femp/purchasing-energy-efficient-light-bulbs
- Size in feet, Length 20, Width 40, Light level Warehouses, corridors, hallways, exitways (5 fc, OSHA), Bulb brightness Type my own, Lumens per bulb 1,000 gives Lumens needed 4,000, Bulbs 4.Source: OSHA 29 CFR 1926.56, Illumination, Table D-3 (minimum foot-candles), https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.56
How it works
- Area = length × width, in square feet (sizes in feet) or square meters (sizes in meters). 1 ft = 0.3048 m exactly, so 1 ft² = 0.09290304 m².
- Light level: a preset in foot-candles, or a typed level in foot-candles or lux. 1 foot-candle = 1 lumen per square foot = 1 ÷ 0.09290304 = 10.7639104 lux.
- Lumens needed = area × light level (square feet × foot-candles, or square meters × lux; both give the same lumens).
- Bulbs = lumens needed ÷ lumens per bulb, rounded up to a whole bulb (exactly 4.0 stays 4).
Presets (OSHA Table D-3, minimum foot-candles):
| Preset | Foot-candles |
|---|---|
| Offices, first aid stations | 30 |
| Shops, equipment rooms, indoor workrooms | 10 |
| Warehouses, corridors, hallways, exitways | 5 |
| General construction areas | 3 |
Bulbs (DOE FEMP Table 2): 450 lumens (40 W incandescent), 800 (60 W), 1,100 (75 W), 1,600 (100 W), or a typed lumens per bulb.
Inputs and limits
- Length and width: 0.1 to 10,000. Typed light level: 0.1 to 100,000. Lumens per bulb: 1 to 1,000,000.
- Typed values are read as exact decimals and every step is exact. Shown values are rounded half up: lumens to whole lumens, light levels and square feet to 1 decimal, square meters to 2 decimals.
Assumptions
All the light reaches the work surface: there is no allowance for fixture efficiency, wall reflectance or dirt.
Worked examples by hand
12 × 12 ft office, 30 foot-candles, 800-lumen bulbs: 144 ft² × 30 = 4,320 lumens. 4,320 ÷ 800 = 5.4, so 6 bulbs. In lux: 30 × 10.7639 = 322.9 lux.
4 × 3 m room at 300 lux, 1,100-lumen bulbs: 12 m² × 300 = 3,600 lumens; 3,600 ÷ 1,100 = 3.27, so 4 bulbs. In foot-candles: 300 × 0.09290304 = 27.9.
20 × 40 ft hallway at 5 foot-candles, 1,000-lumen bulbs: 800 × 5 = 4,000 lumens; 4,000 ÷ 1,000 = exactly 4 bulbs.
Other questions people ask
How many lumens do I need for a room?
Multiply the floor area by the light level you want. In US units, lumens = square feet × foot-candles; in metric, lumens = square meters × lux. A 12 × 12 ft room at 30 foot-candles needs 144 × 30 = 4,320 lumens.
What is a foot-candle?
One lumen spread over one square foot. One lux is one lumen over one square meter, so 1 foot-candle = 10.764 lux (NIST).
How many lumens is a 60 watt bulb?
The Department of Energy lists 800 lumens as the match for a 60 W incandescent bulb, 450 for 40 W, 1,100 for 75 W and 1,600 for 100 W. LED bulbs are sold by lumens, so check the package.
Where do the light levels come from?
The presets are OSHA’s minimum illumination for construction work (29 CFR 1926.56): 30 foot-candles for offices and first aid stations, 10 for shops and indoor workrooms, 5 for hallways and warehouses and 3 for general outdoor areas. They are minimums for work, not design levels for a home; type your own level for other rooms.
Why does my room look darker than the calculation?
The calculation assumes every lumen lands on the surface you light. Dark walls, lampshades, fixture losses and dust absorb some of it, so a room usually needs more lumens than the plain product.