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How to Calculate Wattage Per Square Foot for Lighting

Power is a measure -- in watts, or joules per second -- of how quickly energy is used. In today's energy-conscious world, estimating energy consumption is a worthwhile task; a standard way to do this is to measure how much energy is being used within a unit of area. The number of watts per square foot can be calculated for lighting using some basic information, such as room size and light power.

Things You'll Need

Tape measure
Calculator

Instructions

- 1
  Measure, in feet, the length and width of the room with a tape measure. Write down the measurements.
- 2
  Multiply the length of the room by the width of the room. This gives the total area of the room in square feet.
- 3
  Check the number of watts being used in the light bulbs in the room. Switch off the light(s) and remove the bulb(s) for examination. The wattage is usually printed on the side of the light bulb; in common usages, wattage usually vary from 50 to a few hundred watts. If you still the original box or container that held the bulb, the wattage should be printed there. When you are finished, reinstall the bulbs in their sockets.
- 4
  Divide the total power from all light bulbs in the room by the area of the room in square feet. This gives wattage per square foot.

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