What Is Lumens per Square Foot?
Lumens per square foot, also called foot-candles (fc), measures how much light actually lands on a surface. While a bulb's lumen rating tells you its total light output, foot-candles tell you the brightness experienced on a desk, floor, or workbench. This calculator divides your total lumens by the area you are lighting to give a clear illuminance value.
How to Use the Calculator
Enter the total lumens of all fixtures in the space and the area you want to light in square feet. The calculator returns the foot-candle level and an equivalent value in lux (the metric unit). Add up the lumen output of every bulb in the room for the most accurate result.
The Formula Explained
The equation is simply $$\text{Foot-Candles} = \frac{\text{Total Lumens}}{\text{Area (ft}^2\text{)}}$$ Because one foot-candle is defined as one lumen per square foot, the division gives the answer directly. To convert to lux, multiply foot-candles by \(10.7639\), since one square meter contains about \(10.76\) square feet.
Worked Example
Suppose a 200 sq ft home office has fixtures producing 8,000 total lumens. $$\text{Foot-Candles} = \frac{8{,}000}{200} = 40\ \text{fc}$$ which is ideal for detailed desk work. In lux that is \(40 \times 10.7639 \approx 431\) lux.
FAQ
How many foot-candles do I need? Living rooms need roughly 10–20 fc, kitchens and offices 30–50 fc, and detailed task areas 50–75 fc.
Is lumens per square foot the same as foot-candles? Yes. A foot-candle is defined as exactly one lumen per square foot.
What is the difference between foot-candles and lux? Both measure illuminance; foot-candles use square feet while lux uses square meters. Multiply foot-candles by \(10.7639\) to get lux.
