Lux to Lumens Calculator

The Lux to Lumens Calculator converts a target illuminance in lux into the total lumens a room needs, using the room's area or its length and width. Beyond the textbook conversion, it also shows a real-world lumen figure that allows for light loss, estimates how many bulbs you need, and places your brightness on a visual lux scale with a to-scale, glowing room diagram — turning "how much light do I need?" into a clear shopping answer.

Lux to Lumens Formula

Lux is illuminance (light landing on a surface) and lumens is luminous flux (total light emitted). One lux equals one lumen spread over one square metre, so the conversion is simply lux multiplied by the lit area:

Because real fixtures never deliver every lumen to the work surface — light is lost to walls, ceiling height, fixture design, and lamp ageing — the lumens you should actually install are higher. Dividing by a utilisation (light-loss) factor gives a practical target:

Lux vs Lumens vs Foot-candles

Lumens tell you how much light a bulb produces in total. Lux tells you how bright a surface is once that light spreads out — the same bulb gives high lux in a small room and low lux in a large one. Foot-candles are the imperial version of lux: one foot-candle is one lumen per square foot, which equals about 10.764 lux.

How to Use This Calculator

1. Set the target lux: Type the illuminance you want, or pick a room type to load a recommended lux level automatically.
2. Enter the room size: Give the length and width, or switch to total area, in metres or feet.
3. Tune the lighting quality: Choose a utilisation factor (100% for the pure conversion, ~80% for a typical room) and the lumens per bulb you plan to use.
4. Click Calculate: Read off the total lumens, the real-world lumens to install, the bulb count, and a to-scale room diagram that brightens with your lux level.

Recommended Lux Levels by Room

These maintained illuminance targets follow common EN 12464-1 and IES lighting guidance. They are sensible starting points — adjust for personal preference, age, and task detail.

Worked Example

Suppose you want 500 lux in a 4 m × 3 m kitchen (12 m²). The core conversion is 500 × 12 = 6,000 lumens. Applying a typical 80% utilisation factor gives 6,000 ÷ 0.8 = 7,500 lumens to install. With 800-lumen LED bulbs, that is ⌈7,500 ÷ 800⌉ = 10 bulbs (or fewer, brighter fixtures).

What Affects How Many Lumens You Need?

Frequently Asked Questions

How do you convert lux to lumens?

Multiply the illuminance in lux by the lit area in square metres: Lumens = Lux × Area (m²). For example, 300 lux over a 20 m² room needs 300 × 20 = 6,000 lumens. If your area is in square feet, convert it to square metres first by multiplying by 0.0929.

What is the difference between lux and lumens?

Lumens measure the total amount of visible light a source emits, while lux measures how much of that light lands on a surface. One lux equals one lumen spread over one square metre. Spreading the same lumens over a larger area lowers the lux, so a bright bulb can still give dim lux in a big room.

How many lumens do I need for a room?

Multiply the recommended lux for the room by its area in square metres. Typical targets are about 150 lux for a bedroom, 200 lux for a living room, 300 lux for a bathroom, and 500 lux for a kitchen or office. A 12 m² kitchen at 500 lux needs roughly 6,000 lumens before allowing for light loss.

Why does this calculator show more lumens than lux times area?

Real rooms lose light to walls, ceiling height, fixture design, and lamp ageing. The utilisation factor divides the ideal lumens by this efficiency (typically about 80%) so you buy enough lumens to actually reach your target lux. Set the factor to 100% for the pure lux × area conversion.

How do I convert lux to foot-candles?

Divide the lux value by 10.764. One foot-candle equals one lumen per square foot, which is about 10.764 lux. For example, 500 lux is roughly 46 foot-candles.

Does bulb wattage matter for this calculation?

No. Only lumens matter for brightness. Wattage tells you energy use, not light output. A modern LED can produce 800 lumens from about 9 watts, while an old incandescent needs around 60 watts for the same 800 lumens. Enter lumens per bulb, not watts, to estimate how many bulbs you need.

Additional Resources

• Lux - Wikipedia
• Lumen (unit) - Wikipedia