Formula
lux = lumens ÷ area (m²)
1 lux is 1 lumen spread evenly over 1 square meter. For area in square feet, the tool converts to m² first (1 ft² = 0.0929 m²).
Worked example
A 1,600 lm LED fixture lighting a 12 m² room evenly: 1600 ÷ 12 = 133 lux — fine for general living-room ambience, but too dim for a workspace (aim for 300–500 lux).
Reference table
Quick reference (even distribution)
| Lumens | Lux over 5 m² | Lux over 10 m² | Lux over 20 m² |
|---|---|---|---|
| 400 | 80 | 40 | 20 |
| 800 | 160 | 80 | 40 |
| 1,600 | 320 | 160 | 80 |
| 3,000 | 600 | 300 | 150 |
| 5,000 | 1,000 | 500 | 250 |
Where this shows up in the real world
Lighting plans, workshop upgrades and the eternal 'is this room too dim?' question all run through lux. US and UK guidance both put offices and kitchens around 300–500 lux and detailed task areas higher — so a 1,600 lm fixture over a 12 m² room (about 130 lux spread evenly) explains precisely why the garage still feels gloomy.
Common mistakes to avoid
The even-spread assumption is the catch: real rooms lose light to walls, dark surfaces and distance, so treat the simple division as a best case and plan 20–40% above target. Don't buy bulbs by watts either — LED efficiency varies wildly; lumens are the light, watts are just the cost.
Frequently asked questions
What lux levels should rooms have?
Common guidance: 100–200 lux for hallways and ambient living areas, 300–500 lux for kitchens, offices and study desks, 500+ lux for detailed task work.
Is this calculation exact for my room?
It assumes light spreads evenly across the area. Real rooms lose light to walls and distance, so treat the result as an upper-bound estimate; professional design uses utilization factors.
Lumens vs lux vs watts?
Watts measure power consumed, lumens measure total light output, lux measures how much light lands on a surface. Efficient LEDs give more lumens per watt.