Lighting Lumens per Room Calculator

How it is calculated

Area is in square metres, the target lighting level is in lux (lumens per square metre) and the output of one fitting is in lumens. The engine calculates total lumens = area × lux, then fittings = ceil(total ÷ lumens per fitting), rounded up to whole fittings, and LED watts = total ÷ 100, which assumes a fixed efficacy of 100 lumens per watt. The tool uses no allowance for wall colour, ceiling height, dirt on the fittings or light lost in shades, so the real brightness at the working surface can be lower. All three inputs must be above zero. The right lux target depends on the room and the task, so choose one for how the space is used.

Common mistakes

• Typing the room area in square feet. The tool expects square metres, so a 215 sq ft room is about 20, not 215.
• Entering the bulb's wattage in the lumens field. A 9 W LED gives roughly 800 lm; the field needs the lumen figure printed on the box.
• Using one lux level for every room. A hallway and a kitchen work area need very different targets, and the total scales directly with the value you pick.
• Treating the watts as the size of one bulb. The wattage is for the whole room; divide by the number of fittings to get the power of each one.
• Expecting an exact brightness at the desk or counter. Dark walls, tall ceilings and shades absorb light, which this calculation does not model, so an extra margin is sensible in such rooms.