How the estimate works
Lighting designers use a rough rule of thumb: a target number of lumens per square metre depending on what the room is for. A bedroom you relax in needs far less than a kitchen where you chop vegetables. We multiply your room's floor area by a sensible lumens-per-square-metre figure for that room and brightness level, then divide by the number of bulbs to tell you how bright each one should be.
Why it's a starting point, not a rule
Real rooms vary. Dark walls and floors absorb light, so you may want to aim higher. A tall ceiling spreads light over more distance — tell us the ceiling height and we'll nudge the figure up. Lots of daylight, pale walls, or plenty of lamps mean you can often go lower. Think of the result as a well-informed baseline you can adjust to taste.
Turning lumens into bulbs
Once you know the lumens you need per bulb, choose LEDs with roughly that lumen rating, in the suggested colour temperature, to match your fittings. For a single replacement bulb rather than a whole room, the bulb finder is quicker. To understand lumens, see what are lumens?