Lighting calculator

How to use

1. Pick the room: Each room type has a foot-candle range for general light.
2. Measure: Room length and width in feet.
3. Set brightness: Low, middle or high end of the range, and an allowance for dark walls or high ceilings.
4. Choose bulbs: Pick the bulb output to see how many you need.

Lumens and foot-candles

A lumen measures how much light a bulb gives off; a foot-candle measures how much reaches a surface. One foot-candle is one lumen spread over a square foot, so the light a room needs is its area times the foot-candles for its use.

Home Depot's guide to estimating lumens gives 10 to 20 foot-candles for living rooms and bedrooms, 30 to 40 for dining rooms, 70 to 80 for bathrooms and the kitchen stove area, 60 to 80 for a home office and 80 to 100 for a garage. Hallways are commonly lit at about 5 to 10.

From lumens to bulbs

LED packaging lists lumens. Home Depot notes that a 60 watt incandescent and a 10 watt LED both give about 800 lumens, and that a 100 watt incandescent gives about 1,500 to 1,700. Divide the room's total by the lumens of the bulb or fixture you plan to use.

Rooms with dark walls or high ceilings may need more light. The calculator's +15% and +30% options are a simple allowance for that, chosen by us; trust your eyes and add dimmers.

How it is calculated

• 1 foot-candle = 1 lumen per square foot
• Lumens = room area (sq ft) × foot-candles for the room × surface factor
• Bulbs = lumens ÷ lumens per bulb, rounded up

Examples

14 × 12 ft living room

168 sq ft × 15 foot-candles (middle of 10–20) = 2,520 lumens, about four 800 lm bulbs. The range for the room is 1,680 to 3,360 lumens.

8 × 10 ft bathroom

80 sq ft × 75 foot-candles = 6,000 lumens, eight 800 lm bulbs. Put most of it at the mirror, where you need it.

Frequently asked questions

How many lumens do I need per square foot?

About 10 to 20 lumens per square foot in living rooms and bedrooms, 30 to 40 in a dining room and 70 to 80 in bathrooms and at kitchen work areas, according to Home Depot's lumens guide. One foot-candle is one lumen per square foot.

How many lumens for a living room?

Multiply the area by 10 to 20. A 14 × 12 ft living room (168 sq ft) needs about 1,700 to 3,400 lumens in total, spread over ceiling light and lamps.

How many lumens is a 60 watt bulb?

About 800 lumens. Home Depot notes that a 60 watt incandescent and a 10 watt LED both give about 800 lumens, and a 100 watt incandescent about 1,500 to 1,700.

Why does a bathroom need so much light?

Shaving, makeup and cleaning are close-up tasks. The 70 to 80 foot-candle figure is mostly needed at the mirror; the rest of the room can be dimmer.

Do dark walls need more light?

Yes. Dark walls and high ceilings reflect less light back into the room; Home Depot's guide says such rooms may need additional lumens. The calculator's +15% and +30% options are our own allowance, not a standard.

How many recessed lights do I need?

Divide the room's lumens by the output of one fixture from its spec sheet. A 168 sq ft living room at 2,520 lumens needs four 650 lm downlights (2,600 lm), placed evenly, plus lamps for reading.

Sources

• How to Estimate Lumens for Your Space, The Home Depot