Lighting Calculator

What is a lighting calculator?

A lighting (lumens) calculator recommends how much light a room needs — measured in lumens and the number of bulbs — based on the room’s size, its purpose, and ceiling height. It converts “this room feels dark” into a concrete shopping list.

How this calculator works

• Enter the room length, width, and ceiling height.
• Pick the room type — living rooms, kitchens, offices, and workshops want different light levels.
• It multiplies area by a foot-candle target to get total lumens.
• Divide by your bulb’s output to get the bulb count; ceiling-height correction is applied for rooms above 8 feet.

How to use the result

1. Use the lumen total, not wattage — LEDs and old bulbs differ wildly in lumens per watt.
2. Match the bulb count to your fixtures; a living room often needs layers (overhead + lamps), not one giant bulb.
3. Add task lighting for reading, food prep, and work surfaces — those areas want more than the room average.
4. For LED replacements, read the lumens on the box — a 60W-equivalent LED is about 800 lumens.

How many lumens do I need per square foot?

Living and bedrooms run about 20 lumens per square foot; kitchens, bathrooms, offices, and garages about 40. A 120 ft² living room therefore wants roughly 2,400 lumens — three 800-lumen bulbs or two 1,200-lumen fixtures. Higher ceilings dilute light, so taller rooms need more.

Common mistakes

• Buying by wattage. A 9W LED and a 60W incandescent can both emit ~800 lumens — compare lumens.
• Under-lighting task areas. One room-wide bulb can’t cover a kitchen counter or a desk.
• Ignoring ceiling height. The same fixture in a 9- or 10-foot ceiling delivers noticeably less light at the surface.

Lighting is about covering a surface area with a usable amount of light — the same area math behind the roofing cost calculator’s square-footage estimates. If you’re finishing a room, the drywall calculator and paint calculator cover the surfaces around those fixtures.