Calculator
What the Illuminance Converter does
Illuminance Converter: 1 lx = 0.09290304 fc, so multiply a lux value by 0.09290304 to get foot-candle, or divide to go back. Example: 500 lx = 46.45152 fc.
From Value, From and To, this tool derives Result, How it was calculated and Reverse conversion. Edit a field and the answer updates in place.
Typical users are people following a recipe or spec written elsewhere. Two industries often use the same word for slightly different quantities.
There is no back end here. The calculation runs where you are sitting, not on a server somewhere.
The method, a field-by-field reference and a worked example built from the defaults are all on this page.
What do the Illuminance Converter fields mean?
The Illuminance Converter uses 3 inputs. Each input has a default that makes sense on its own, so a partial edit still gives a valid result.
| Field | What to enter | Default |
|---|---|---|
| Value | required | 500 |
| From | choose from Lux (lx), Kilolux (klx), Phot (ph), Foot-candle (fc) or Nox (nox) | Lux (lx) |
| To | choose from Lux (lx), Kilolux (klx), Phot (ph), Foot-candle (fc) or Nox (nox) | Foot-candle (fc) |
How does the Illuminance Converter work?
Both units are converted through illuminance's base unit (lx), so any of the 5 units in the dropdowns can be paired in either direction without loss of accuracy.
Factors follow the internationally agreed definitions. The inch has been exactly 25.4 mm since 1959, and an exact definition is used wherever one exists. Where a unit is fixed by measurement rather than by agreement, the accepted CODATA or IAU value is used.
Worked example
These are the values the Illuminance Converter loads by default, and the result it produces from them. Here is the calculation as it stands the moment the page loads.
| Value | 500 |
|---|---|
| From | Lux (lx) |
| To | Foot-candle (fc) |
| Result | 46.45152 fc |
|---|---|
| How it was calculated | 1 lx = 0.09290304 fc, so 500 × 0.09290304 = 46.45152 fc |
| Reverse conversion | 5381.955208 lx (if you meant 500 fc) |
Illuminance: lux and foot-candles
1 foot-candle equals exactly 10.763910417 lux (not a simple round 10, which is a very common rounding mistake), because a foot-candle is defined per square foot while lux is defined per square metre, and a square metre is considerably larger than a square foot.
Worth knowing
- Everyday reference points help make sense of the scale: typical office lighting is roughly 300 to 500 lux, an overcast day outdoors might be 1,000 to 10,000 lux, direct sunlight can exceed 100,000 lux, and full moonlight is only around 0.1 to 1 lux. A range spanning roughly six orders of magnitude.
- Lux is the standard unit worldwide for lighting design and photography light-meter readings, while foot-candles remain common specifically in US architectural and lighting-industry specifications.
- Because the conversion factor isn’t a round number, mentally approximating with "×10" instead of the precise 10.76 introduces a small but real error that compounds in lighting-design calculations, where illuminance targets are often specified to meet a specific building code or standard.
Definitions: BIPM SI Brochure · NIST reference on units
How to use it
- Fill in Value.
- Pick a value for From: the options are Lux (lx), Kilolux (klx), Phot (ph), Foot-candle (fc) or Nox (nox).
- Pick a value for To: the options are Lux (lx), Kilolux (klx), Phot (ph), Foot-candle (fc) or Nox (nox).
- Watch the results panel as you type: it recalculates on every keystroke.
- The panel reports Result, How it was calculated and Reverse conversion.
- Copy Link is the quickest way to send the exact scenario to someone else.
What this tool does not do
- Repeated conversions compound rounding, so convert once from the original value where you can.
- Conversion factors use SI definitions; some industries use their own rounded factors.
- The output is a number, not a judgement. Deciding what it means is still your job.
- Confirm the units before you act on the output. The arithmetic is only as sound as what went in.
Frequently asked questions
Only Value, From and To. Nothing starts empty, which means a single edit is enough to get a meaningful answer.
With the values loaded when the page opens, result comes out as 46.45152 fc. Any edit re-runs the calculation, so there is no stale number on screen.
Nothing leaves your machine. The only network traffic is loading the page itself.
Nothing at all. There is no registration, no paywall and no per-use quota.
It matches what you would get working it out by hand, with fewer opportunities to slip.