How to Calculate kWh for Lighting

You can calculate your Kilowatt Hour costs for lighting from your energy bill summary based on a simple formula. Survey your home or business and calculate each lighting fixture power output in kWh and cost associated with them per month. In most cases, the power company will penalize you for using power during peak months and peak hours. Read on to find out how to calculate kWh used for lighting throughout your home or business.

Things You'll Need

• Power bill
• Calculator

Instructions

1. You can use your monthly bill to break down the cost of kWh for lighting.
   Example:
   1. Total Bill = $150.00
   2. kWh total = 1060
   3. Cost per Hour Breakdown for the Month = $150.00 (Total Bill)/1060(kWh) = $0.141509 per Kilowatt Hour used

2. The following formula will let you calculate the cost of your lighting.
   Example: You have a 60 watt light bulb that is on 9 hours a day in a 30 day month.
   9 hours a day x 30 days = 270 hours in a 30 day month used
   270 hours x 60 watts = 16,200 watt hours used by the single light bulb
   kWh = 1000 watts
   16,200 watts/1000 watts = 16.2 kWh used

3. You can calculate how much this single light bulb cost you on your bill.
   16.2 kWh x $0.141509 = $2.292446 or about $2.29 used by the light bulb in a 30 day period.

4. When you are breaking down the cost of your lighting, remember to count all light bulbs if you have a light fixture with multiple light bulbs.
   Example:
   A fixture has 5 light bulbs that produce 60 watts.
   5 x 60 = 300 watts total for the fixture
   You can plug this into Step 2 and Step 3 to calculate the kWh use and cost for the total light fixture.

References

• Wikipedia kWh Formula
• PG&E Definition for kWh Prices (click on first link for Excel spreadsheet)
• Merriam-Webster Definition of kWh