Convert illuminance between lux (lx) and foot-candles (fc) in one step, with easy rounding and plain or scientific number display. This helps you match a light meter, a classroom problem, or a spec sheet without guesswork.
Advanced options
How to use our Lux to Foot Candles Converter Calculator
- Choose the conversion direction (Lux to foot-candles, or Foot-candles to lux).
- Type the value you want to convert. You may use scientific notation like 3.41e-4.
- Open Advanced options if you need specific rounding or formatting.
- Pick a Rounding style: Significant figures (good for measurements) or Decimal places (good for fixed-format reports).
- If using Significant figures, set the Significant figures count. If using Decimal places, set the Decimal places count.
- Choose a Display format: Auto, Plain, or Scientific. Auto switches to scientific notation only when values are very small or very large.
- If Display format is Auto, adjust the small and large thresholds (they must be positive numbers).
- (Optional) Turn on the quick reference table to sanity-check common values.
- Click Calculate, then copy the single-line result from the Copy-ready output.
Definitions
Illuminance: How much light lands on a surface area (not how much light a lamp makes).
Lux (lx): Illuminance per square meter.
Foot-candle (fc): Illuminance per square foot.
Conversion direction: Which unit you start with and which unit you want as the answer.
Significant figures: The count of meaningful digits in a measurement (example: 0.09290 has 4 significant figures).
Decimal places: The count of digits after the decimal point (example: 46.451 has 3 decimal places).
Scientific notation: A way to write very large or very small numbers like 1.23e-6.
Lumens vs illuminance: Lumens measure total light output; lux and foot-candles measure light on a surface. You cannot convert lux or fc to lumens without knowing the area.
Methodology
What gets converted
Lux and foot-candles are both illuminance units, so the conversion depends only on area units (square meters vs square feet) and does not require any assumptions about a lamp or distance.
Core conversion factors
fc = lx / 10.7639104167
lx = fc * 10.7639104167
The number 10.7639104167 is the square-foot per square-meter factor (rounded for display). It comes from the space and time unit relationships in ISO 80000. [1]
Where 10.7639104167 comes from
Using the exact international foot definition (1 ft = 0.3048 m), the area ratio is the square of the length ratio.
1 m^2 = (1/0.3048)^2 ft^2
Evaluating (1/0.3048)^2 gives 10.7639104167097... which is shown as 10.7639104167 in this calculator and then used consistently. [1]
Rounding and display rules (what the calculator does)
raw_converted = input_value * factor
If Rounding style is Significant figures, the calculator rounds the raw result to the chosen count of significant figures. If Rounding style is Decimal places, it rounds to the chosen count of digits after the decimal point.
Display format controls how the (rounded) number is shown: Plain uses normal decimals, Scientific uses e-notation, and Auto switches to scientific when the absolute value is smaller than the small threshold or larger than the large threshold. Auto thresholds must be positive.
Edge cases and notes shown in results
If the input is blank or not a valid number (including invalid e-notation), the calculator shows an error and does not compute results. If the computed value is not finite (NaN or Infinity), it also shows an error.
Negative inputs are allowed for math (the sign is preserved), but the Notes output reminds you that real-world illuminance readings are normally non-negative.
The Notes output also calls out a common mix-up: lux and foot-candles measure illuminance, but lumens measure total light output, so you cannot convert to lumens without an area. Terms follow ISO quantity-and-unit conventions. [2]