Lumen Requirement Calculator
When the Preset Room Types Don't Fit
A standard room-type lighting guide covers the common cases, but a home theater, a hobby workshop, or a plant-growing nook doesn't map cleanly onto "living room" or "garage." This calculator drops the presets and lets you specify the exact foot-candle target you're designing for, converting any illumination requirement directly into a total lumen budget for the space.
The Formula
Once you have the total lumens needed, dividing that figure by a single fixture's rated lumen output tells you roughly how many fixtures the space requires.
Where This Calculation Matters
- Specialty and hobby spaces — a craft room, workshop, or home gym often needs a specific foot-candle target pulled from task-lighting guidance rather than a general room-type default.
- Matching a lighting designer's specification — if you've been given a target foot-candle level from a professional plan, this calculator converts it straight into a lumen and fixture-count budget.
- Combining ambient and task lighting — calculating the base ambient requirement separately from added task lighting (like under-cabinet or desk lighting) keeps the two budgets distinct and easier to plan.
- Retrofitting existing fixtures — comparing a room's current total fixture lumen output against the calculated requirement shows whether existing lighting is under- or over-specified.
Lumens Needed by Foot-Candle Target
For a 12 ft × 15 ft (180 sq ft) room at different foot-candle targets:
| Foot-candles | Total lumens needed |
|---|---|
| 10 (general hallway level) | 18,000 |
| 20 (general room level) | 36,000 |
| 35 (kitchen task level) | 63,000 |
| 50 (workshop/garage level) | 90,000 |
How to Use This Calculator
- Enter Room Length and Room Width (ft).
- Enter the Required Foot-Candles for your specific space or task.
- Select Calculate to see the total lumens needed for that lighting level.
Related Calculations
Looking for standard room-type recommendations instead of a custom target? See the Interior Lighting Design Calculator, or plan the room's layout around the new fixtures with the Interior Design Space Planner.