Lighting Calculator
Calculate how many lumens and bulbs a room needs based on its size and how bright the space should be.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Estimate lumens as floor area in square feet multiplied by the target illuminance you enter in foot-candles. Choose a target appropriate to the activity and lighting plan; this simple estimate does not account for ceiling height, wall reflectance, fixture losses, glare or code requirements.
Worked example
calculated with the default values below
Room length 12 ft · Room width 12 ft · Target illuminance 70 fc · Lumens per bulb 800 lm Room area 144.0 sq ft · Lumens needed 10,080 lm · Bulbs needed 13
General background references
Disclaimer
These calculators provide planning estimates only. Building codes, wiring regulations and safety requirements differ by country and change over time, and nothing here replaces a licensed professional or a permit. For structural, electrical or gas work, follow local code and have the installation inspected.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
area = length × width; lumensNeeded = area × targetFc; bulbs = ceil(lumensNeeded ÷ bulbLumens)
- L
- room length (ft)
- W
- room width (ft)
- lumens
- total lumens needed
- bulbs
- bulbs needed (rounded up)
- lumens_per_bulb
- lumens provided by one bulb
- targetFc
- user target illuminance (foot-candles)
Area = length × width (sq ft); lumens = area × user-entered foot-candle target; bulb count rounds up. This is a planning estimate, not a lighting standard.
Frequently asked questions
How should I choose the target illuminance?
Enter the foot-candle target for the task and lighting plan you are using. The calculator applies that value uniformly across floor area; it does not specify a code-compliant or room-standard target.