Convert between lux and foot-candles. Calculate total lumens for an area, luminous exitance, and compare illuminance levels for different environments.
Lux and foot-candles are both units of illuminance — the amount of light falling on a surface — but they belong to different measurement systems. Lux (SI) measures lumens per square meter, while foot-candles (Imperial) measure lumens per square foot. The conversion factor is 1 fc = 10.764 lux. Despite the metric system's dominance in science, foot-candles remain standard in US building codes, IESNA lighting recommendations, and real estate specifications.
Architects, lighting designers, and facility managers constantly convert between these units when specifying lighting levels, evaluating compliance with codes, or comparing international standards. Office lighting standards typically call for 300-500 lux (28-46 fc), while surgical suites may require 1,500+ lux (140+ fc). Photographers use the conversion for exposure calculations across equipment calibrated in different systems.
This calculator performs bidirectional lux/foot-candle conversion, computes total luminous flux (lumens) needed for a given area, estimates reflected light (exitance) based on surface reflectance, and provides comprehensive reference tables for common illuminance levels. The illuminance scale bar provides instant visual context from moonlight to direct sunlight.
Use this calculator when a lighting spec, code reference, or fixture sheet switches between SI and US illuminance units.
It is useful for room-lighting design, facilities work, photography, and quick lumen estimates where the target light level matters more than the lamp wattage. It also keeps the area-based lumen estimate in the same place as the illuminance conversion, which makes it easier to compare a room target with a fixture specification.
Foot-candles = Lux / 10.764. Lux = Foot-candles × 10.764. Total lumens = Lux × Area(m²). Exitance = Illuminance × Reflectance.
Result: 46.45 fc, 10,000 lumens total
500 lux ÷ 10.764 = 46.45 fc. To illuminate 20 m² at 500 lux: 500 × 20 = 10,000 lumens needed. With 50% reflectance, exitance = 250 lux.
Lux and foot-candles describe the same physical idea, so the important question is not which unit is better but which target level suits the space. Offices, classrooms, retail counters, and inspection benches all need different illuminance ranges, and that target should drive the conversion.
The biggest mistake is converting the number correctly but applying it to the wrong reference plane or task. Floor area, desk height, beam spread, and surface reflectance all affect the real lighting outcome. Treat the total-lumens estimate as a planning tool, not as a substitute for a full fixture layout.
US building codes (IES, ASHRAE), real estate, and many American industries use foot-candles. OSHA workplace lighting standards are also in foot-candles.
General office: 300-500 lux (28-46 fc). Detailed work: 500-1000 lux. Computer screens: 300 lux is usually sufficient to avoid glare.
It is the amount of light leaving (reflected from) a surface. Exitance = illuminance × reflectance. A white wall (ρ≈0.8) reflects much more light than a dark floor (ρ≈0.1).
1 foot-candle = 10.76391 lux, exactly. This comes from 1 lumen/ft² = 1 lumen/(0.3048² m²) = 10.7639... lumens/m².
At higher altitudes, there's less atmosphere to scatter light. Illuminance on a clear day can reach 120,000+ lux at 3000m elevation versus ~100,000 lux at sea level.
Yes, most smartphones have ambient light sensors. Apps like "Lux Meter" provide reasonable readings, though professional lux meters are more accurate and calibrated.