Turn a target illuminance level and room area into the total lumen budget a lighting design needs to hit it.

How to Use the Lux to Lumens Calculator

Enter the illuminance target in lux and the floor area in square meters. The lumen figure below is the total luminous flux that combination requires.

Building codes and workplace lighting standards specify illuminance, not lumens — an office might need 500 lux, a warehouse aisle 150 lux, a hallway 100 lux. None of that tells you how many bulbs to buy. What a supplier or electrician actually needs is a lumen budget for the room, and that's a straight multiplication once you have the target and the floor area.

lm = lux × area (m²)

A 20 m² office held to 500 lux needs 10,000 lumens delivered across the space — split across, say, four fixtures rated at roughly 2,500 lumens apiece, before accounting for losses from fixture efficiency and mounting height that this flat area-based figure doesn't model. A dimmer hallway target of 100 lux over that same 20 m² only calls for 2,000 lumens, a fifth as much — the formula scales linearly however the numbers move. Manufacturers sometimes call this a "lumen method" calculation, and it's the first number a lighting designer works out before ever picking specific fixtures — fixture count, wattage, spacing, all trace back to it.

This is a starting budget, not a final fixture count. Real designs also weigh wall and ceiling reflectance and fixture spacing, neither of which factors into a flat lux-times-area figure.