Lux to Footcandle Calculator - lx to fc with lm/m^2 Cross-Check

A lux to footcandle calculator is a photometric converter that turns a light-level reading expressed in lux (lumens per square meter) into the equivalent foot-candle value (lumens per square foot), or runs the same calculation in reverse. It is most useful when you have a sensor or specification sheet in one unit and need to read or quote the value in the other without re-doing the math by hand. You can use it to translate a European data sheet into the foot-candles that a United States lighting designer asks for, or to sanity-check a lux meter against a foot-candle target.

• • Translate sensor readings: Read a lux meter on a workbench and quote the same level in foot-candles for an architect or broadcast client.
• • Match IES recommended levels: Compare IES recommended illuminance ranges (often listed in both lx and fc) against what your fixtures actually deliver at the task plane.
• • Verify lighting designs: Spot-check a photometric simulation by hand without re-opening the design software.
• • Support classroom demonstrations: Show students how the same physical quantity looks different in SI versus United States customary units.

Lux and foot-candles describe the same physical quantity, illuminance, in two different units. The two units exist because most of the world adopted the SI lux in 1960 while United States lighting practice, photography, and broadcast television kept using the older foot-candle. The conversion between them is exact and comes from the international foot, so the math is the same every time.

If you have a room area and bulb lumens instead of a single illuminance reading, Lighting Calculator combines area, lux, and bulb output to size a fixture layout.

The calculator applies a single conversion factor that comes from the exact definition of the international foot. Pick a direction, enter the illuminance value, and the same factor multiplies or divides your input to give the matching result.

• Illuminance value: The reading in lux or foot-candles, depending on the chosen direction. Must be zero or positive.
• Conversion factor: Lux per foot-candle, default 10.7639104167. Editable so you can compare rounded factors.
• Direction: Either luxToFc (divide by the factor) or fcToLux (multiply by the factor).

Because lux and foot-candles measure the same quantity, the lm/ft^2 and lm/m^2 secondary outputs let you read the value in either system no matter which direction you picked. If those numbers look swapped, you have likely inverted the direction without changing the input label.

According to NIST, the international foot is defined as exactly 0.3048 m, so one square foot is exactly 0.09290304 m^2 and one foot-candle equals 10.7639104167 lux. That single line of geometry is the entire source of the conversion factor.

According to NIST Special Publication 811, the international foot is defined as exactly 0.3048 m, so one square foot is exactly 0.09290304 m^2 and one foot-candle equals 10.7639104167 lux.

When the illuminance has to be traced back to a source, Luminosity Calculator turns radius and temperature or flux and distance into watts so the photometric chain stays consistent.

Four ideas show up every time you compare lux and foot-candles. Knowing them makes the calculator easier to trust and easier to explain to someone else.

If you want a deeper look at how luminous flux becomes a luminance value on a screen or panel, Luminance Converter works the other side of photometry and converts cd/m^2 into nits and foot-lamberts.

The lux to footcandle calculator is built for fast on-site work. The default direction is lux -> fc because most international meters read in lux.

1. 1 Pick a direction: Choose lux -> fc if your reading is in lux (the common SI direction) or fc -> lx if you are starting from a United States light meter.
2. 2 Enter the illuminance value: Type the reading in the numeric field. The default 500 lx is the IES general office target so the page opens with a useful value.
3. 3 Confirm the conversion factor: Leave the factor at 10.7639104167 unless you are deliberately testing a rounded approximation.
4. 4 Read the converted value: Use the primary result for the answer in the opposite unit. The label switches between fc and lx automatically.
5. 5 Cross-check in lm/ft^2 and lm/m^2: Confirm that the secondary outputs match the physical scene you measured; both should describe the same surface lighting.
6. 6 Reset to the office default: Click Reset to return to 500 lx and the exact factor for the next reading.

A facilities engineer measures 750 lx above a school desk. Direction lux -> fc, value 750, factor 10.7639104167. The calculator returns 69.677 fc and 750 lm/m^2, which is comfortably above the IES 500 lx classroom minimum and lets the engineer quote the result to the architect in either unit.

When you want to see why a given illuminance corresponds to a certain color temperature, Blackbody Radiation Calculator shows the spectral exitance of a blackbody at that temperature.

A purpose-built lux to footcandle calculator saves time on every step of a lighting project and removes the most common arithmetic slips.

• • One tool, both directions: Switch between lux to fc and fc to lx without reloading the page or hunting for the inverse factor.
• • Cross-checked output: Side-by-side lm/ft^2 and lm/m^2 rows make it obvious whether the value you typed matches the surface you actually measured.
• • Editable factor: The 10.7639104167 factor can be replaced with a rounded 10.76 or 10.8 to see how textbook approximations change the result.
• • Reference illuminance levels: The factors and limitations sections list IES recommended levels so the calculator doubles as a quick lighting reference card.
• • Audit-friendly math: The pure calculateResults function returns the same three numbers you would compute by hand, which is useful for design reviews and classroom checks.

If you want to keep working in lumens once you have a foot-candle value, Lumens to Watts Calculator turns bulb lumens and luminous efficacy into watts so the lighting design can be matched to the available fixtures.

The arithmetic is exact, but the answer is only as good as the reading you type and the unit conventions behind the reference levels you compare it to.

• • The calculator assumes a flat, evenly lit surface. Specular highlights and directional sources give readings that depend strongly on meter orientation.
• • Lux and foot-candles are photopic quantities. They do not describe UV, infrared, or photosynthetic photon flux density (PPFD), which need different meters and units.
• • Rounded factors like 10.76 or 10.8 give the same answer to three significant figures but start to drift when comparing large values such as direct sunlight (~100 000 lx).

The IES Lighting Library publishes reference illuminance levels for offices, classrooms, hospitals, and outdoor tasks in both lux and foot-candles. Use those as the target band, not the lux to footcandle calculator's default value.

According to Illuminating Engineering Society (IES) Lighting Library, IES recommended horizontal illuminance for general office work is about 500 lux, which is roughly 46 foot-candles.

According to Wikipedia, Foot-candle, one foot-candle is the illuminance of one lumen per square foot, exactly equal to 10.7639104167 lux, and the unit remains common in United States architectural and broadcast practice.

Once you have settled on a fixture wattage, Ohm's Law Calculator pairs voltage and current so the driver sizing and circuit planning stay grounded in real numbers.