OneTaskBy Tim King · Updated
Lumens Calculator
How Many Lumens and Bulbs a Room Needs
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How the Lumens Calculator works
This lumens calculator tells you how much light a room needs. Enter the room's length and width in metres or feet, pick what the room is used for and the lumens of the bulb you plan to fit, and it returns the total lumens, how many bulbs or downlights that takes, the light level in lux or foot-candles and a rough LED wattage.
Lumens measure the light a bulb gives out. Lux measures how much of that light lands on each square metre of floor; one foot-candle is one lumen per square foot, about 10.76 lux. Rooms need different levels: a bedroom is comfortable at about 100 lux, a kitchen worktop wants 300, and a home office or workshop wants 500 for close work.
How the lumens calculator works
The formula is lumens = floor area × target lux. For example, a 4 m × 3.5 m living room is 14 m², and at 150 lux it needs 14 × 150 = 2,100 lumens, which is three 800-lumen bulbs. A second example in feet: a 12 × 10 ft kitchen is 120 ft², and at 30 foot-candles (about 300 lux) it needs 3,600 lumens, or five 800-lumen downlights.
This is a simple planning figure. Dark walls, high ceilings and lampshades absorb light, so add 20–30% for a room with dark décor or ceilings above 2.7 m (9 ft). Layered lighting spreads the total across ceiling lights, lamps and task lights rather than one fitting.
To decide how many downlights to fit, divide the total lumens by the output of the downlight you like, then space them evenly, roughly half the ceiling height apart from each other and a quarter of that from the walls. LEDs give around 80–110 lumens per watt, so the watts shown are for LED; an old incandescent bulb gave only about 12 lumens per watt.
Lumens needed by floor area and room type (150, 300 and 500 lux)
| Floor area | 150 lux (living room) | 300 lux (kitchen) | 500 lux (office) |
|---|---|---|---|
| 4 m² (43 ft²) | 600 lm | 1,200 lm | 2,000 lm |
| 6 m² (65 ft²) | 900 lm | 1,800 lm | 3,000 lm |
| 8 m² (86 ft²) | 1,200 lm | 2,400 lm | 4,000 lm |
| 10 m² (108 ft²) | 1,500 lm | 3,000 lm | 5,000 lm |
| 12 m² (129 ft²) | 1,800 lm | 3,600 lm | 6,000 lm |
| 14 m² (151 ft²) | 2,100 lm | 4,200 lm | 7,000 lm |
| 16 m² (172 ft²) | 2,400 lm | 4,800 lm | 8,000 lm |
| 18 m² (194 ft²) | 2,700 lm | 5,400 lm | 9,000 lm |
| 20 m² (215 ft²) | 3,000 lm | 6,000 lm | 10,000 lm |
| 24 m² (258 ft²) | 3,600 lm | 7,200 lm | 12,000 lm |
| 28 m² (301 ft²) | 4,200 lm | 8,400 lm | 14,000 lm |
| 32 m² (344 ft²) | 4,800 lm | 9,600 lm | 16,000 lm |
| 36 m² (388 ft²) | 5,400 lm | 10,800 lm | 18,000 lm |
| 40 m² (431 ft²) | 6,000 lm | 12,000 lm | 20,000 lm |
| 44 m² (474 ft²) | 6,600 lm | 13,200 lm | 22,000 lm |
| 48 m² (517 ft²) | 7,200 lm | 14,400 lm | 24,000 lm |
| 52 m² (560 ft²) | 7,800 lm | 15,600 lm | 26,000 lm |
| 56 m² (603 ft²) | 8,400 lm | 16,800 lm | 28,000 lm |
| 60 m² (646 ft²) | 9,000 lm | 18,000 lm | 30,000 lm |
| 64 m² (689 ft²) | 9,600 lm | 19,200 lm | 32,000 lm |
FAQ
How many lumens do I need for a living room?
Allow about 150 lux, which is 150 lumens per square metre or roughly 15 per square foot. A 20 square metre living room needs around 3,000 lumens in total, spread across ceiling lights and lamps so you can dim the room for evenings.
How many lumens is a 60 watt bulb?
An old 60 W incandescent bulb gave about 800 lumens, so an 800-lumen LED is the usual replacement and draws 8–10 watts. A 40 W equivalent is around 470 lumens and a 100 W equivalent is about 1,600 lumens.
What is the difference between lumens and lux?
Lumens are the total light a bulb emits in every direction. Lux is the light arriving on a surface, in lumens per square metre. The same 800-lumen bulb gives high lux in a small room and low lux in a large one because the light is spread further.
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