Lumens to Lux Calculator
Enter the luminous flux in lumens and the room or surface area in square metres to find the illuminance in lux — the number that tells you how bright a space actually feels.
Works for any light source
The formula lx = lm divided by m² applies to any lamp, fixture, or floodlight. Enter the rated lumens from the packaging and the area you want to illuminate to get the average illuminance.
Assumes even distribution
This calculation treats the light as perfectly spread over the entire area. Real fixtures have beam angles and distance effects, so actual lux at a point will vary. See the limitations section for details.
What is lux?
The unit that measures how much light reaches a surface
Lux (lx) is the SI unit of illuminance — it measures how much luminous flux (lumens) falls on each square metre of a surface. One lux equals one lumen per square metre. While lumens describe the total output of a light source, lux describes how bright that light makes a specific surface. Spreading the same number of lumens over a larger area reduces the lux proportionally, which is why a 1,000-lumen bulb can light a small bathroom to 200 lx but leave a large living room at only 40 lx.
Enter the lumens and the area in m² to find the illuminance in lux instantly.
Divide the luminous flux in lumens by the area in square metres to get the illuminance in lux.
lx = lm ÷ m²To work the example: a standard 800-lumen LED distributed over 10 m² gives 800 ÷ 10 = 80 lx. If the same bulb illuminates only a 4 m² desk area, the result is 800 ÷ 4 = 200 lx — more than enough for relaxed reading. Doubling the lumens to 1,600 lm over the original 10 m² doubles the illuminance to 160 lx.
The lux figure tells you the average illuminance over the area you entered, assuming the light is spread evenly. Reference levels give context for whether the result is appropriate for the intended use. A corridor or stairwell needs around 100 lx for safe navigation. A living room typically requires 150–300 lx for comfortable general lighting. A kitchen or office workspace needs 300–500 lx for practical tasks such as cooking or reading documents. Detailed work — craft, drawing, or surgical lighting — calls for 750–1,000 lx or more. If the calculator returns a value well below the target range, add more lumens, reduce the area, or use multiple fixtures. A value far above the target is not harmful but may indicate over-lighting, which wastes energy and can cause glare.
This calculator gives an average illuminance based on the assumption that all lumens are evenly distributed across the stated area.
Real lighting is not perfectly uniform
Actual fixtures have beam angles, mounting heights, and reflector designs that concentrate light in some areas and leave others dimmer. Lux at a point on the floor directly below a downlight is far higher than lux in the corners of the same room. For accurate point-by-point calculations, use photometric software with the fixture's IES or LDT file. The result here is a useful planning estimate, not a photometric guarantee.