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Quickly convert illuminance units including lux (lx), foot-candles (fc), and phots (ph).
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
Illuminance describes luminous flux arriving at a surface per unit area. Lux (lx) is one lumen per square meter; a foot-candle (fc) is one lumen per square foot. They express the same kind of quantity using different area units, so converting a reading changes its numerical value and unit label, not the measured lighting condition. The Federal Highway Administration glossary gives these definitions for lux and foot-candle.
For the main conversion, use the factor listed by NIST: 1 fc = 10.76391 lx. In the other direction, divide lux by 10.76391. For example, 50 lx is about 4.6452 fc, while 10 fc is about 107.6391 lx. The quick mental estimate of 1 fc ≈ 10 lx is convenient, but the more precise factor is better when comparing recorded values.
The converter treats lux as its base for the calculation and displays results for the selected input across its available illuminance units. NIST also lists 1 phot (ph) = 10,000 lx. NIST Guide to the SI, Appendix B.9 supports these conversion factors; the FHWA glossary explains the underlying illuminance units. Both sources checked October 2, 2026.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Enter the number from an existing illuminance reading or document. Choose the unit that the number already uses, such as lx or fc.
Read the matching result in the displayed unit groups. The form shows converted values for the available units, rather than requiring a separate target-unit calculation.
Set the precision selector if you need a different number of decimal places. Click a result to use it as the new input, or copy the displayed number for a note or worksheet.
Keep the unit symbol beside every copied value. For instance, record “50 lx ≈ 4.6452 fc,” rather than saving “4.6452” by itself.
Use cases
See how the tool fits into real work and everyday tasks.
If a lighting document states a level in lux but a meter record uses foot-candles, convert one value before placing both in the same comparison. Keep the original number and unit so the source remains clear.
When a team collects readings or design notes using different unit conventions, convert them to the shared unit chosen for the worksheet. The converted figures make unit labels consistent; the team still decides how to interpret the readings.
Use a measured lux value to obtain a foot-candle equivalent, or convert a foot-candle value back to lux, without estimating by mental arithmetic. This is a conversion of a value you already have, not a light-meter reading.
Q&A
Find concise answers to common questions and confusing cases.
One foot-candle is 10.76391 lux in the NIST conversion table. A rounded estimate is 10.76 lx per fc; multiplying by 10 is a rougher shortcut.
Divide the lux value by 10.76391. For example, 50 lx ÷ 10.76391 is approximately 4.6452 fc. To convert fc to lx, multiply by 10.76391.
No. Lumens describe luminous flux, while lux describes that flux per unit area. You need the relevant illuminated area and distribution information to determine illuminance; this converter changes between illuminance units only.
The precision control rounds the displayed result to the selected number of decimal places and removes trailing zeros. Keep the original reading for traceability, and use the precision required by your report or specification.
Notes
Review scope, result limitations, and important precautions before use.
A unit conversion does not measure a room, predict light from a fixture, or determine whether a workplace, roadway, or other space meets a requirement. Those judgments depend on the measurement method, location and orientation of the sensor, applicable specification, and other project conditions. Use an appropriate meter and the governing document when evaluating actual lighting.
The menu includes a nox label. Its calculation uses the same factor as millilux in this converter; the NIST references above do not establish that mapping as an authoritative definition. Avoid relying on that label for a standards-based report without independently confirming the required unit and convention. Results are rounded for display, so retain the unrounded source reading when precision matters.
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