# How many lumens do I need?

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.

- Page: https://www.acalculator.org/construction/lumens-calculator
- JSON spec: https://www.acalculator.org/construction/lumens-calculator.json
- Version: 26c62562e3ff

## Default answer

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.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| u | Size in | Feet or meters for the room size. |
| l | Length | The room or area length. |
| w | Width | The room or area width. |
| t | Light level | A minimum light level from OSHA’s table, or your own target. |
| lv | Target light level | The light you want on the work surface, in the unit chosen next. |
| lu | Light level in | Foot-candles (lumens per square foot) or lux (lumens per square meter). |
| b | Bulb brightness | The light output of each bulb, in lumens. |
| pb | Lumens per bulb | The lumens printed on the bulb’s package. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| lumens | Lumens needed | Area × light level: foot-candles × square feet, or lux × square meters. |
| bulbs | Bulbs | Lumens needed ÷ lumens per bulb, rounded up to a whole bulb. |
| fc | Light level (foot-candles) | The target in foot-candles (lumens per square foot). |
| lux | Light level (lux) | The target in lux (lumens per square meter). |
| sqft | Area (ft²) | Length × width in square feet. |
| sqm | Area (m²) | Length × width in square meters. |

## Method

lumens = area × light level (ft² × foot-candles, or m² × lux); bulbs = lumens ÷ lumens per bulb, rounded up.

## Assumptions

- 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

1. u = ft, l = 12, w = 12, t = office, b = 800 gives lumens = 4,320, bulbs = 6, fc = 30, lux = 322.9, sqft = 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.
2. u = m, l = 4, w = 3, t = custom, lv = 300, lu = lux, b = 1100 gives lumens = 3,600, bulbs = 4, sqm = 12, fc = 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.
3. u = ft, l = 20, w = 40, t = hall, b = custom, pb = 1,000 gives lumens = 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.

## FAQ

### 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.

## Sources

- OSHA, 29 CFR 1926.56 Illumination, Table D-3: minimum illumination intensities in foot-candles. https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.56 (retrieved 2026-10-19)
- NIST Special Publication 811, Appendix B.9: footcandle and lumen per square foot to lux, × 10.76391; 1 ft = 0.3048 m exactly. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9 (retrieved 2026-10-19)
- NIST Special Publication 811, Chapter 4, Table 3: the lux is one lumen per square meter. https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-4-two-classes-si-units-and-si-prefixes (retrieved 2026-10-19)
- US Department of Energy, Federal Energy Management Program, Purchasing Energy-Efficient Light Bulbs, Table 2: 450, 800, 1,100 and 1,600 lumens for 40, 60, 75 and 100 W incandescent bulbs. https://www.energy.gov/cmei/femp/purchasing-energy-efficient-light-bulbs (retrieved 2026-10-19)