How much electricity costs, and how they charge you

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How much electricity costs, and how they charge you What is a kilowatt hour? When you buy gas they charge you by the gallon. When you buy electricity they charge you by the kilowatt-hour (kWh). When you use 1000 watts for 1 hour, that's a kilowatt-hour. For example: Device wattage

Device

42" ceiling fan on low speed 24 watts

Hours used

kWh

ten hours

0.24 kWh

light bulb

100 watts

730 hours (i.e., all month)

73 kWh

CFL light bulb

25 watts

730 hours

18 kWh

When the number is low we sometimes use watt-hours (Wh) instead of kWh. For example, we might say 240 watthours instead of 0.24 kWh. Watts and watt-hours Watts is the measure of the rate of electrical use at any moment. For example, a laptop computer uses about 50 watts. Understand the difference between watts and watt-hours: • Watts is the rate of use at this instant. • Watt-hours is the total energy used over time. Here is an example of watts vs watt-hours. "You say that some device uses 100 watts. What period of time is that for?" It's not for any period of time, because watts is a rate at that instant. One might as well ask: "The speedometer in my car says I'm going 35 miles an hour. What period of time is that for?" It's not for any period of time. You're going 35 miles an hour at that instant. To measure use over a period of time, we use watt-hours, not watts. The way it works is, watts or kilowatts for the amount at a given instant, and watt-hours or kilowatt-hours for the amount over a period of time.