This lighting calculator finds how many lumens a room needs: floor area times the recommended footcandle level for the room’s job — then translates lumens into bulbs.
| Total lumens needed | – |
| Bulbs / fixtures at that output | – |
| LED watts (at ~100 lm/W) | – |
Footcandle targets are mid-range residential recommendations (IES-style guidance): 1 footcandle = 1 lumen per sq ft by definition, which is why the math is a single multiplication. Dark walls, tall ceilings and older eyes all argue for the top of each range — and dimmers forgive oversizing, never undersizing.
Lumens = Footcandles × Square Feet — Light Is an Area Dose
Room sizing’s other half (cooling) is our Air Conditioner BTU Calculator. Part of our Construction Calculators collection.
Worked Example (Verified)
- Kitchen, 180 sq ft at 40 footcandles (defaults): 7,200 lumens = nine 800-lumen bulbs, or six 1,200-lumen recessed fixtures — and the counter-task layer at 75 fc wants its own under-cabinet contribution on top
- The incandescent ghost: 7,200 lumens used to mean ~720 W of heat-pumping glass; LED does it at ≈ 72 W — lighting went from a top-three home energy load to a rounding error in one technology step
- Living-room contrast: the same 180 sq ft at 15 fc needs only 2,700 lumens — kitchens are workshops, living rooms are theaters, and the footcandle table is the script
Layering Discipline
- Ambient (this calculator’s total) + task (counter, desk, mirror) + accent (art, shelving): the total is a budget to distribute, not a single fixture’s job.
- Uniformity beats raw lumens: four mid fixtures read brighter than one blazing center light with cave corners.
- Color temperature is atmosphere’s dial: 2700–3000K living spaces, 3500–4000K kitchens/offices — matching CCT across a room matters more than the last 200 lumens.
- Aging eyes need roughly double the light at 60 vs 20 for the same task — design the grandparents’ reading chair accordingly.
Related Tools
- AC BTU Calculator — cooling for the same room
- LED Savings Calculator — what the switch saves
- Construction Calculators — the full collection
Frequently Asked Questions
How many lumens does a room need?
Multiply floor area by the footcandle target for the room’s use — lumens = fc × sq ft because 1 footcandle is exactly 1 lumen/sq ft. A 180 sq ft kitchen at 40 fc needs 7,200 lumens; a same-size living room at 15 fc needs 2,700. This calculator holds the target table by room type.
What is a footcandle?
The illuminance from one lumen spread over one square foot (the metric twin is the lux, per square metre: 1 fc ≈ 10.764 lux). Recommended residential levels run 10 fc (hallways) to 75 fc (kitchen counters, detailed task work).
How many lumens is a 60W bulb?
A 60 W incandescent made ≈ 800 lumens — still the reference “bulb” in most lighting math, and what a 9–10 W LED now matches. 100 W incandescent ≈ 1,600 lumens (≈ 15 W LED). This calculator lets you set any per-bulb output.
Why does my calculated room still feel dark?
Lumens are emitted, not perceived: dark surfaces absorb (a charcoal room can swallow half the light), high ceilings dilute, and bare downlights pool light in circles leaving gloom between. Raise the total 25–50% for dark finishes, spread fixtures wider, and add wall-washing — the formula starts the conversation.
Is brighter always better in kitchens and offices?
Up to the glare limit: past ~75 fc without shielding, contrast and reflections fatigue eyes faster than darkness did. Layer task light where hands work, keep ambient moderate, and put it on dimmers — control is the luxury feature, raw lumens are just the budget.
Is this lighting calculator free?
Yes — free, instant, no sign-up.