Case 1
- Target illuminance (lx)
- 500lx
- Lit area (m²)
- 20m²
10,000lm
Open with these valuesLux to Lumens Calculator
10,000lm
Result: 10,000 lmMultiply the illuminance by the lit area: lighting 20 m² to 500 lx needs 10000 lumens. Lux already means lumens per square metre, so the area only scales it up to a total. Double the room and you need twice the lumens for the same brightness.
The numbers at a glance
Held fixed: Target illuminance (lx) 500.0 lx.
| Lit area (m²) (m²) | Result (lm) |
|---|---|
| 5.00 | 2,500 |
| 10.00 | 5,000 |
| 15.00 | 7,500 |
| 20.00Your value | 10,000 |
| 25.00 | 12,500 |
| 30.00 | 15,000 |
| 35.00 | 17,500 |
| 40.00 | 20,000 |
Worked examples
Case 2
- Target illuminance (lx)
- 300lx
- Lit area (m²)
- 12.5m²
3,750lm
Open with these valuesCase 3
- Target illuminance (lx)
- 1000lx
- Lit area (m²)
- 2.5m²
2,500lm
Open with these valuesHow it's calculated
lumens = lux × area in m²
- StepPick the illuminance the room needs — 300–500 lx for an office.
- StepMeasure the floor or work surface in square metres.
- ResultMultiply; the result is the total lumens all fixtures must deliver.
Reference table
| Lux, area | What that covers | Lumens |
|---|---|---|
| 100, 1 | One square metre at hallway level | 100 |
| 300, 12.5 | A small bedroom | 3750 |
| 500, 20 | A 20 m² office at standard level | 10000 |
| 750, 8 | A brightly lit shop counter | 6000 |
| 1000, 2.5 | A workbench under task lighting | 2500 |
Questions
How do I convert lux to lumens?
Multiply the illuminance in lux by the lit area in square metres. Lighting a 20 m² room to 500 lx needs 500 × 20 = 10000 lumens. Lux already means lumens per square metre, so the area simply scales it up to a total.
What is the difference between lux and lumens?
Lumens measure luminous flux, the total amount of visible light a source emits. Lux measures illuminance, how much of that light lands on each square metre of a surface. One lux is one lumen per square metre, so lux depends on both the output and the area it has to cover.
Why does the area change how many lumens I need?
Because lux is lumens per square metre. To keep the same brightness over a bigger surface the light has to spread further, so the total has to rise. Double the area and you need twice the lumens for the same lux.
What units should I use?
Lux for the illuminance and square metres for the area, which gives the flux in lumens. If your area is in square feet, divide by 10.7639 to get square metres first. The result is the total the whole installation must deliver.
How accurate is this?
The formula is exact, but it assumes the illuminance is uniform across the area and ignores beam angle, mounting height and distance. Real fixtures light the centre more than the edges. Treat the result as a total-lumens target and place the fixtures so the light spreads evenly.
Sources and last check
Information, not professional advice.