Quick answer
Illuminance units convert through lux. 1 foot-candle equals 10.7639 lux (one lumen per square foot versus per square metre).
Enter a value and choose the units. The calculator returns the converted illuminance.
Related tools: Volume Converter: Convert litres, gallons, cups, spoons and more. Weight Converter: Convert kilograms, pounds, ounces, stone and more. Length Converter: Convert between metric and imperial lengths.
How to use the Illuminance Converter
- Enter value.
- Choose from: Lux (lx), Kilolux (klx), Foot-candle (fc) and Phot (ph).
- Choose to: Lux (lx), Kilolux (klx), Foot-candle (fc) and Phot (ph).
- Enter decimal places (between 0 and 10). It starts at 4.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Value | A number | — |
| From | Choose one: Lux (lx); Kilolux (klx); Foot-candle (fc); Phot (ph) | Starts at Lux (lx) |
| To | Choose one: Lux (lx); Kilolux (klx); Foot-candle (fc); Phot (ph) | Starts at Kilolux (klx) |
| Decimal places | A number | ≥ 0, ≤ 10, starts at 4 |
Formula and method
Formula
result = value × (factor of source ÷ factor of target), base unit: lux
IEEE-754 double precision; displayed to the chosen number of decimal places (default 4). Very small or large results are shown in scientific notation.
Every unit is defined by an exact or published factor to the base unit (lux). The value is multiplied by the source factor and divided by the target factor.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Value = 1; From = Foot-candle (fc); To = Lux (lx); Decimal places = 4.
| Result | Value |
|---|---|
| Foot-candle (fc) → Lux (lx) | 10.7639 |
| Input | 1 Foot-candle (fc) |
Example 2
Inputs: Value = 1; From = Lux (lx); To = Foot-candle (fc); Decimal places = 6.
| Result | Value |
|---|---|
| Lux (lx) → Foot-candle (fc) | 0.092903 |
| Input | 1 Lux (lx) |
Example 3
Inputs: Value = 1; From = Phot (ph); To = Kilolux (klx); Decimal places = 4.
| Result | Value |
|---|---|
| Phot (ph) → Kilolux (klx) | 10 |
| Input | 1 Phot (ph) |
The first line is the headline result (foot-candle (fc) → Lux (lx)). Below it the illuminance Converter lists input, which describe the same case from other angles. IEEE-754 double precision; displayed to the chosen number of decimal places (default 4). Very small or large results are shown in scientific notation.
Unit reference
Each unit expressed in the base unit used for the calculation. Conversions go through this base unit, so any unit can be converted to any other in the table.
| Unit | Equals (in lux) |
|---|---|
| Lux (lx) | 1 |
| Kilolux (klx) | 1000 |
| Foot-candle (fc) | 10.76391042 |
| Phot (ph) | 10000 |
Typical light levels
Moonlight is below 1 lux, a living room 50 to 150 lux, an office 300 to 500 lux and full daylight 10,000 to 100,000 lux. 30 foot-candles is about 323 lux.
Illuminance versus luminance
Illuminance is light arriving on a surface (lux), while luminance is light leaving it (cd/m²). They are different quantities and need different converters.
How the result changes with value
Holding every other input at the first worked example, this table changes only value. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Value | Foot-candle (fc) → Lux (lx) | Input |
|---|---|---|
| 0.5 | 5.382 | 0.5 Foot-candle (fc) |
| 1 | 10.7639 | 1 Foot-candle (fc) |
| 2 | 21.5278 | 2 Foot-candle (fc) |
| 4 | 43.0556 | 4 Foot-candle (fc) |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Value: left empty shows "Enter value." beside that field and no result.
Choosing between the Illuminance Converter and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Volume Converter](/converters/volume-converter/) | value, from and to | US gallon → Litre (L) |
| [Weight Converter](/converters/weight-converter/) | value, from and to | Pound (lb) → Gram (g) |
| [Length Converter](/converters/length-converter/) | value, from and to | Mile (mi) → Kilometre (km) |
| [Energy Converter](/converters/energy-converter/) | value, from and to | Megawatt-hour (MWh) → Kilowatt-hour (kWh) |
| [Power Converter](/converters/power-converter/) | value, from and to | Horsepower (mechanical) → Watt (W) |
Background: unit conversion
Many customary units are defined exactly in terms of metric ones: since the 1959 International Yard and Pound Agreement an inch is exactly 2.54 cm and a pound is exactly 0.45359237 kg (NIST SP 811 lists these). So most length and mass conversions are exact apart from the rounding of the displayed result.
To convert, multiply the value by the source unit's factor to reach the base unit, then divide by the target unit's factor; the unit table on this page lists every factor used. Temperature and fuel economy are the exceptions, because they are not simple multiples.
Assumptions and limitations
- Negative values are allowed
- Zero converts to zero (except L/100 km, where zero is invalid)
- Units from different quantities cannot be converted
- Very large or tiny results switch to exponent notation
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for value to confirm this.
Frequently asked questions
How do I convert lux to foot-candles?
Divide lux by 10.764.
What is a lumen?
A unit of total light output.
How bright should an office be?
About 300 to 500 lux.
What does the Illuminance Converter calculate?
Convert lux, foot-candles and phot. It returns Foot-candle (fc) → Lux (lx) and Input.
What formula does the Illuminance Converter use?
result = value × (factor of source ÷ factor of target), base unit: lux. Every unit is defined by an exact or published factor to the base unit (lux).
What does the “From” option change?
It sets how the illuminance is worked out. The choices are Lux (lx), Kilolux (klx), Foot-candle (fc) and Phot (ph).
What is an example of a illuminance result?
With value 1, from Foot-candle (fc), to Lux (lx) and decimal places 4, the foot-candle (fc) → Lux (lx) is 10.7639.
Where does the method come from?
The method follows: NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B (foot-candle, phot and lux conversion factors).
Related calculators
- Volume Converter — Convert litres, gallons, cups, spoons and more.
- Weight Converter — Convert kilograms, pounds, ounces, stone and more.
- Length Converter — Convert between metric and imperial lengths.
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- Power Converter — Convert watts, kilowatts, horsepower and BTU per hour.
- Temperature Converter — Celsius, Fahrenheit, Kelvin and Rankine.
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B (foot-candle, phot and lux conversion factors)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.