About the Lumens Calculator
Lighting is specified in lux — lumens per square metre — and every room type has a recommended level. Multiply the target lux by the floor area and divide by the fittings’ efficiency and you have the total lumens you need. This calculator does that and converts it into bulbs.
Also known as: how many lumens do i need, lumens for a room, lighting calculator, brightness calculator, lux to lumens.
How to use this calculator
- Enter room length, room width, room type, utilisation factor and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
lumens = target lux × area ÷ utilisation factor
Worked example
Using the values pre-filled in the calculator above:
- Room length = 5 m
- Room width = 4 m
- Room type: Kitchen (300 lux)
- Utilisation factor = 0.6
- Lumens per bulb = 800
the calculator returns:
- Total lumens needed: 10,000 lm
- Bulbs required: 13
- Floor area: 20 m²
- Target illuminance: 300 lux