# Energy Efficiency Vocabulary Lesson 1: Kilowatts and Kilowatt Hours

Posted by Luke Fishback

In general at VisibleEnergy we try to explain efficiency concepts in the most relatable terms like dollars, but on occasion it is helpful to talk more specifically about energy usage with the proper vernacular. In this first terminology lesson I will cover the language used on your electricity bill, namely kilowatts (kw) and kilowatt hours (kwh).

A kilowatt is a unit of power. This means that it is an instantaneous measure of consumption rate. To be specific, a kilowatt is a thousand watts. A watt is a joule per second. And a joule is a unit of energy. So, kilowatts are a measure of energy used per time. To use a familiar simile, kilowatts are like miles per hour in your car. Kilowatts tell you how fast you are using energy.

Kilowatt hours are a unit of energy (like calories). One kilowatt hour is the amount of energy used when something consumes one kilowatt of power for one hour, or when something uses 2 kilowatts for a half hour, 500 watts for two hours, etc. If kilowatts were shown on your homes “speedometer,” kilowatt hours would appear on the odometer. Kilowatt hours tell you how much total energy you have used, like the odometer shows you how many miles you’ve traveled.

Most utility companies charge a fixed rate for each kilowatt hour of energy used. On average in America, we pay about 11 cents per kilowatt hour of electricity. So, when you use 1500 kwh in a month, the utility company charges you 1500 x $0.11 = $165. Got it? If not, please tell me in the comments.