Lux to Lumens Calculator
Enter a light level in lux and the area it covers to get the total luminous flux in lumens — and see why a bigger room needs proportionally more light.
From lux to lumens in one step
Enter the illuminance in lux and the lit area in square metres and the calculator returns the total luminous flux in lumens (lumens = lux × area).
Use square metres
Lux is lumens per square metre, so the area must be in square metres — divide square feet by 10.764 to get square metres before you start.
What is the lux to lumens calculator?
Illuminance times area
The lux to lumens calculator turns a light level on a surface into the total amount of light that lands on it. Lux measures illuminance — how brightly a surface is lit — and is defined as lumens per square metre. Lumens measure luminous flux, the total quantity of visible light a source puts out. Because lux is already a "per square metre" figure, the total flux over a surface is just the illuminance multiplied by the area it covers. Enter the lux you want and the area in square metres, and the calculator tells you how many lumens you need to deliver it — the starting point for choosing bulbs, fixtures, or LED panels for a room.
Enter an illuminance in lux and an area in square metres to get the total luminous flux in lumens instantly.
Luminous flux is the illuminance multiplied by the area, because lux is defined as lumens per square metre.
lumens = lux × areaThe relationship is linear in both inputs: double the target lux and you double the lumens, and double the area and you double the lumens too. Use square metres for the area and the flux comes back in lumens, ready to compare against the rated output printed on a bulb or fixture.
Suppose you want to light a 20 m² living room to an office-style 500 lx.
Note the target illuminance
500 lx — the light level you want on the surface.
Note the area
20 m² — the size of the surface being lit.
Multiply the two
500 × 20 = 10,000 lm — the total luminous flux you need to install.
The result is the total luminous flux your lighting must deliver to reach the chosen lux over the whole area. In the example above, 10,000 lumens spread evenly over 20 m² gives 500 lx everywhere. The key insight is that lux is lumens per square metre, so the total flux scales directly with the area: the same bulb that brightly lights a small bathroom will leave a large living room dim, because its fixed lumen output is spread over more square metres. That is why a bigger space needs proportionally more lumens for the same perceived brightness, and why manufacturers quote both a lumen rating (total output) and recommend a lux target (level on the surface). Read the lumen total off your fixtures, add them up, and compare against the figure here to see whether a room is over- or under-lit.
The formula is exact, but it assumes an idealised, evenly lit surface.
Assumes uniform illuminance over the area
This calculator assumes the illuminance is uniform across the whole area and ignores beam angle, mounting height, and distance from the source. Real fixtures throw more light directly below them and less toward the edges, and flux drops with the square of distance, so a single lamp rarely lights a room evenly. Use the result as a total-lumens target, then choose fixtures and placement that spread the light, rather than expecting one bulb to hit the figure everywhere.