Lighting Calculator
Work out how much light a room needs. Enter length and width in feet, pick the room type (each has a foot-candle target), set your bulb's lumens, and get total lumens, the number of bulbs, and the LED wattage that delivers it.
Example: with Room length (ft) 12 · Room width (ft) 12 · Room type (target) Kitchen, general (35 fc) · Lumens per bulb 800 → Target light output: 5,040 lumens (144 sq ft × 35 fc).
- Bulbs needed7 bulbs at 800 lm each
- Power to run it≈ 56 W of LED (vs ≈ 336 W incandescent)
Computed by the calculator below using its default values. Change any input to see your own numbers.
Lumens = square feet × foot-candles (1 fc = 1 lumen per sq ft). An 800-lumen bulb is the classic 60-watt equivalent; modern LEDs deliver about 90 lumens per watt.
Foot-candles, lumens, and why room type matters
Lighting design starts with foot-candles: one foot-candle is one lumen landing on each square foot. Multiply the room's area by its foot-candle target and you have the lumens the fixtures must deliver. The targets used here — around 15 fc for relaxing spaces, 35 for kitchens, 75 for task zones like vanities and counters — follow the recommended illuminance ranges of the IES Lighting Handbook as they are commonly applied to homes. They are conventions, not code.
Divide total lumens by your bulb's output for a fixture count. An 800-lumen LED (the 60 W-equivalent) is the standard unit of household light; at roughly 90 lumens per watt, a 5,000-lumen kitchen costs about 56 watts of LED versus well over 300 watts in incandescent.
How it’s calculated
Target lumens = length × width (sq ft) × foot-candle target (1 fc = 1 lm/sq ft; presets from IES-recommended home illuminance ranges: hallway 8, living 15, kitchen 35, office 45, workshop 50, task 75). Bulbs = lumens ÷ lumens per bulb, rounded up. Wattage estimated at 90 lm/W for LED and 15 lm/W for incandescent.
Assumes 8–9 ft ceilings, lightish walls, and even fixture spacing — dark finishes, tall ceilings, or heavy shades can raise the requirement 20–50%.
Foot-candle targets by room
| Room | Target (fc) | Lumens for 120 sq ft |
|---|---|---|
| Hallway | 8 | 960 |
| Living room / bedroom | 15 | 1,800 |
| Kitchen (general) | 35 | 4,200 |
| Home office | 45 | 5,400 |
| Garage / workshop | 50 | 6,000 |
| Bath vanity / kitchen task | 75 | 9,000 |
IES Lighting Handbook recommended ranges as commonly applied to residences; lumens = 120 sq ft × target.
Common mistakes
- Buying bulbs by watts — watts measure power draw, lumens measure light. An 800 lm LED and an 800 lm incandescent light the room identically.
- Lighting a kitchen to living-room levels: task spaces want 2–5× the foot-candles of lounging spaces.
- Ignoring ceiling height — a 12 ft ceiling spreads the same lumens over more distance, so add fixtures or output.
- Putting the whole count on one dimmer circuit and calling it layered lighting; ambient, task, and accent should switch separately.
Frequently asked questions
How do I calculate lumens for a room?
Multiply square footage by the foot-candle target: lumens = area × fc. A 12 × 12 kitchen at 35 fc needs 144 × 35 = 5,040 lumens, about seven 800-lumen bulbs.
What is a foot-candle?
One lumen of light falling on one square foot of surface. It measures illuminance — light arriving at the counter or floor — while lumens measure what the bulb emits.
How many lumens is a 60-watt bulb?
About 800 lumens. That is the benchmark ' 60 W equivalent' printed on LED packaging; the LED itself draws only 8–10 watts.
Do dark walls change the answer?
Yes. These targets assume typical light finishes; dark paint and open-shade fixtures absorb light, so plan 20–50% more lumens or add task lighting where it counts.
Are these lighting levels required by code?
No — residential codes mostly govern switch placement and efficacy, not brightness. The foot-candle figures are IES-based design guidance for comfortable, functional rooms.