# Lighting Calculator (Lumens per Room)

URL: https://speedycalculator.com/calculators/everyday-life/lighting/
Last updated: 2026-10-25

> The lighting calculator works out how many lumens a room needs for its use – from 100 lux in hallways to 750 lux for kitchen worktops – and how many bulbs or fixtures of a given brightness you need.

## Inputs

- Room / activity (lux)
- Custom illuminance (lux)
- Room length (m, ft, cm, in)
- Room width (m, ft, cm, in)
- Bulb brightness

## Results

- Room area
- Illuminance used
- Lumens needed
- Bulbs needed
- Approximate LED watts in total

## Formula

```
Lumens needed = illuminance (lux) × area (m²)
1 foot-candle = 10.764 lux
Bulbs = ceil(lumens ÷ lumens per bulb)
```

## Explanation

Illuminance, measured in lux (lumens per square metre) or foot-candles, is how bright a surface is lit. Recommended levels depend on the task: relaxing needs far less light than chopping vegetables or sewing. Dark walls and high ceilings absorb light, so add 10–20% in those rooms.

### How to use the Lighting Calculator

- **Room / activity (lux)**
- **Custom illuminance**
- **Room length**
- **Room width**
- **Bulb brightness**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Choose the room and activity (or enter a custom lux level), enter the room length and width and the lumens of the bulbs you plan to use.

### Tips

- Use the figures from your own bills and product labels – prices and appliance ratings vary widely.
- Look at yearly totals: small daily costs add up and make it easier to compare options.
- Round quantities up to whole packs, rolls or bulbs when you shop.
- Re-check the numbers when prices change; most results scale directly with the unit price.

### Common mistakes to avoid

- Confusing watts (power) with watt-hours or kilowatt-hours (energy).
- Comparing prices without bringing them to the same unit first.
- Ignoring one-off costs such as installation, delivery or replacement parts.

### Inputs explained

FieldWhat to enterRoom / activity (lux)Choose one: Living room – general (150 lux), Living room – reading / task (400 lux), Kitchen – general (300 lux), Kitchen – worktop task (750 lux) …Custom illuminanceIn luxRoom lengthUnits: m, ft, cm, inRoom widthUnits: m, ft, cm, inBulb brightnessChoose one: 450 lm (40 W equivalent), 800 lm (60 W equivalent), 1,100 lm (75 W equivalent), 1,600 lm (100 W equivalent) …

### What each result means

- **Room area** = [Room length]×[Room width]
- **Lumens needed** = [Illuminance used]×[Room area]
- **Bulbs needed** = ceil([Lumens needed]÷[Bulb brightness] - 0.000001)
- **Approximate LED watts in total** = [Lumens needed]÷100

### Example values

How the main result changes when **Custom illuminance** changes and everything else stays at the example values above:

Custom illuminance (lux)Lumens needed (lm)1504,2002254,2003004,2003754,2004504,2006004,200

## Worked example

Inputs — Room / activity (lux): Kitchen – general (300 lux); Custom illuminance: 300 lux; Room length: 4 m; Room width: 3.5 m; Bulb brightness: 800 lm (60 W equivalent).

Results — Room area = 150.7 ft²; Illuminance used = 300 lux; **Lumens needed = 4,200 lm**; Bulbs needed = 6; Approximate LED watts in total = 42 W.

## FAQ

**How many lumens does a living room need?**
About 150 lux for general lighting – a 20 m² (215 ft²) room needs about 3,000 lumens.

**How many lumens for a kitchen?**
About 300 lux overall and 500–750 lux on worktops.

**What is the difference between lux and lumens?**
Lumens measure the light a bulb emits; lux measure how much light lands on each square metre.

**What formula does the Lighting Calculator use?**
Lumens needed = illuminance (lux) × area (m²).


## Sources

- [Illuminating Engineering Society – Recommended illuminance values](https://www.ies.org/)