Room Lighting Calculator

Lumens measure the total amount of visible light emitted by a source. Unlike watts (which measure energy consumption), lumens measure actual brightness. Choosing the right lumen output for a room prevents both under-lit dim spaces and harsh, eye-straining over-lit ones.

The formula: Required Lumens = Room Area (sq ft) × Foot-Candles Needed

Foot-candles this calculator uses, by room:

These sit deliberately toward the upper end of the usual published bands. The older figures, which put a living room at 10 to 20 foot-candles, were written for incandescent lighting, when brightness meant heat and a real electricity bill. LED made light cheap, and rooms lit to those old numbers now read as gloomy to most people.

Worked example: Kitchen measuring 12 ft × 14 ft = 168 sq ft at 75 foot-candles: Required lumens = 168 × 75 = 12,600 lumens

A 60W-equivalent LED bulb produces about 800 lumens. Bulbs needed = 12,600 / 800 = 15.75, so 16 bulbs, which in practice means a few multi-head fixtures and under-cabinet strips rather than sixteen ceiling cans.

Metric equivalent: 1 foot-candle = 10.764 lux, so a 75 foot-candle kitchen is roughly 800 lux. Going the other way, divide lux by 10.764. If you work in square meters, multiply the area by the lux figure directly and you get the same lumen total.

Bulb reference (LED equivalents):

• 40W equivalent: ~450 lumens
• 60W equivalent: ~800 lumens
• 75W equivalent: ~1,100 lumens
• 100W equivalent: ~1,600 lumens

Layer your lighting: general ambient, task light over counters and desks, and accent light on art and shelves. The task and accent layers each run at roughly 30 to 50% of the ambient level.