Lumens to Lux Calculator

How it is calculated

The tool divides luminous flux by area: lux = lumens ÷ area, with flux in lumens (lm) and the lit area in square metres (m²). The result is the average illuminance in lux (lx), shown with two decimals. It assumes all the light is spread evenly over that one area, with nothing lost to walls, shades, absorption or light falling outside the area, and it ignores the distance and angle of the source. Lumens may be zero (giving 0.00 lx) but cannot be negative; the area must be above zero, otherwise no result is shown. Real readings from a light meter will usually be lower, and uneven across the surface.

Common mistakes

• Entering the area in square feet. The field is square metres, so convert first (divide ft² by about 10.76) or the lux figure comes out roughly ten times too high.
• Using the bulb's watts instead of its lumens. Wattage measures power consumption, and the lumen rating is on the bulb's packaging.
• Expecting the figure to match a light-meter reading. The tool gives an ideal average with no losses, so measured values are usually lower.
• Confusing lux with foot-candles; one foot-candle is about 10.76 lux, so the two are not interchangeable.
• Adding lumens of lights that point at other areas. Count only the light that actually lands on the surface you entered.