Molly Ayala
Understanding how much electricity your home appliances consume can help you save money on your electricity bills. Units of electricity measure the amount of energy consumed and are calculated in kilowatt-hours (kWh). One unit of electricity is equal to one kilowatt-hour (kWh) of electricity used. For example, a 100-watt bulb kept on for 10 hours will consume one kilowatt-hour of electricity, or one unit. The price of electricity varies depending on the locality and the customer's consumption profile.
| Characteristics | Values |
|---|---|
| Unit Symbol | kW⋅h or kW h |
| Common Representation | kWh |
| Non-SI Unit of Energy | 3.6 megajoules (MJ) |
| Watt-hour | 1,000 Wh |
| Megawatt-hour (MWh) | 1 million Wh |
| Milliwatt-hour (mWh) | 1/1,000 Wh |
| Average Consumption in the US (2020) | 893 kWh per month |
| Energy to Boil 1 Litre of Water | 0.1 kWh |
| Energy Used by 12-watt LED Lamp in 24 hours | 0.3 kWh |
| Energy Used by 12-watt LED Lamp per Month | 9 kWh |
| Energy Produced by a Healthy Adult Male Manual Laborer in 8 hours | 0.5 kWh |
| Unit Price | Depends on the customer's consumption profile over time and locality |
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What You'll Learn
Kilowatt-hour (kWh) is a non-SI unit of energy
The kilowatt-hour (kWh) is a non-SI unit of energy equal to 3.6 megajoules (MJ) in SI units. It is the energy delivered by one kilowatt of power for one hour. Kilowatt-hours are a common billing unit for electrical energy supplied by utilities. Metric prefixes are used for multiples and submultiples of the basic unit, the watt-hour (3.6 kJ). The kilowatt-hour is a composite unit of energy equal to one kilowatt (kW) multiplied by, or sustained for, one hour.
The International System of Units (SI) unit of energy is the joule (symbol J). Because a watt is, by definition, one joule per second, and because there are 3,600 seconds in an hour, one kWh equals 3,600,000 joules or 3.6 MJ. A widely used representation of the kilowatt-hour is kWh, derived from its component units, kilowatt and hour.
Kilowatt-hours are commonly used by electrical energy providers for billing purposes, as the monthly energy consumption of a typical residential customer ranges from a few hundred to a few thousand kilowatt-hours. Megawatt-hours (MWh), gigawatt-hours (GWh), and terawatt-hours (TWh) are often used for metering larger amounts of electrical energy for industrial customers and in power generation.
The unit price of electricity charged by utility companies may depend on the customer's consumption profile over time. Prices vary considerably by locality. Kilowatt-hours are a product of power and time, not a rate of change of power with time. Electrical energy is typically sold to consumers in kilowatt-hours, with the cost of running an electrical device calculated by multiplying the device's power consumption in kilowatts by the operating time in hours and the price per kilowatt-hour.
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kWh is equal to 3.6 megajoules (MJ)
A kilowatt-hour (kWh) is a non-SI unit of energy equal to 3.6 megajoules (MJ). Kilowatt-hours are a common billing unit for electrical energy supplied by utilities. They are a product of power and time, not a rate of change of power with time. An electric heater consuming 1,000 watts (1 kilowatt) operating for one hour uses one kilowatt-hour of energy.
Kilowatt-hours and megajoules are both units used to measure energy. A kilowatt-hour is a measure of electrical energy equal to one kilowatt, or 1,000 watts, of power over a one-hour period. Kilowatt-hours are a measure of electrical work performed over a period of time, and are often used as a way of measuring energy usage by electric companies.
The kilowatt-hour is a composite unit of energy equal to one kilowatt (kW) multiplied by (i.e. sustained for) one hour. The International System of Units (SI) unit of energy is the joule (symbol J). Because a watt is, by definition, one joule per second, and because there are 3,600 seconds in an hour, one kilowatt-hour equals 3,600 kilojoules or 3.6 megajoules.
Kilowatt-hours are sometimes converted to megawatt-hours per year (MWh/yr), gigawatt-hours/year (GWh/yr), or terawatt-hours per year (TWh/yr). These units are used to express major energy production or consumption over a given period, often a calendar or financial year.
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kWh is a common billing unit for electrical energy
A kilowatt-hour (kWh) is a unit of energy used to bill delivered energy to customers by electric utility companies. It is commonly used in billing for delivered energy to consumers by electric utility companies, and in commercial, educational, and scientific publications, and in the media. It is also the usual unit representation in electrical power engineering.
The kilowatt-hour is commonly used by electrical energy providers for billing purposes since the monthly energy consumption of a typical residential customer ranges from a few hundred to a few thousand kilowatt-hours. Kilowatt-hours are a product of power and time, not a rate of change of power with time. The cost of running an electrical device is calculated by multiplying the device's power consumption in kilowatts by the operating time in hours and the price per kilowatt-hour.
The unit price of electricity charged by utility companies may depend on the customer's consumption profile over time. Prices vary considerably by locality. In the United States, prices in different states can vary by a factor of three. While smaller customer loads are usually billed only for energy, transmission services, and the rated capacity, larger consumers also pay for peak power consumption, the greatest power recorded in a fairly short time, such as 15 minutes.
Kilowatt-hours are a common billing unit for electrical energy supplied by electric utilities. Metric prefixes are used for multiples and submultiples of the basic unit, the watt-hour (3.6 kJ). The kilowatt-hour is a composite unit of energy equal to one kilowatt (kW) multiplied by (i.e., sustained for) one hour. The International System of Units (SI) unit of energy is the joule (symbol J). Because a watt is by definition one joule per second, and because there are 3,600 seconds in an hour, one kWh equals 3,600 kilojoules or 3.6 megajoules (MJ).
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The unit price of electricity varies by locality
The kilowatt-hour (kWh) is the basic unit of electricity. One kilowatt-hour is equal to the energy delivered by one kilowatt of power for one hour. Kilowatt-hours are a common billing unit for electrical energy supplied by utilities.
Electricity prices are dependent on many factors, such as the price of power generation, government taxes or subsidies, CO2 taxes, local weather patterns, transmission and distribution infrastructure, and multi-tiered industry regulation. For instance, electric utilities that have a high percentage of hydroelectricity tend to have lower prices, while those with many older coal-fired power plants tend to have higher prices. Fuel prices, especially for natural gas and petroleum fuels, may increase during periods of high electricity demand and when fuel supply constraints or disruptions occur due to extreme weather events or accidental damage to transportation infrastructure.
Demand for electricity also contributes to the cost of supplying it. Electricity demand is usually highest in the afternoon and early evening (peak hours), so costs are typically higher at these times. Most consumers pay prices based on the seasonal average cost of electricity, so they do not experience these daily price fluctuations. Some utilities offer their customers time-of-day pricing to encourage electricity conservation and reduce peak demand.
The cost to supply electricity varies minute by minute. The wholesale price of electricity on the electric power grid reflects the real-time cost of supply. In standard regulated monopoly markets like the United States, multilevel governance structures set electricity rates through a regulatory process overseen by governmental organizations.
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1 kWh = 3,600 kilojoules
One unit of electricity is one kilowatt-hour (kWh). This is equal to the energy delivered by one kilowatt (1,000 watts) of power over one hour. Kilowatt-hours are a common billing unit for electrical energy supplied by utilities.
Kilowatt-hours are a measure of electrical work performed over a period of time and are often used as a way of measuring energy usage by electric companies. They are a product of power and time, not a rate of change of power with time.
Kilowatt-hours and kilojoules are both units used to measure energy. There are 3,600 kilojoules in one kilowatt-hour. This is because a watt is defined as one joule per second, and there are 3,600 seconds in an hour.
The International System of Units (SI) unit of energy is the joule, and the kilowatt-hour is a non-SI unit. One kilowatt-hour is equal to 3.6 megajoules in SI units.
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Frequently asked questions
A unit of electricity is a measure of the amount of energy consumed at a property.
Units of electricity are measured in kilowatt hours (kWh). One unit of electricity is equal to one kilowatt hour (kWh) of electricity used.
The cost of a unit of electricity depends on the energy supplier and tariff. In the UK, rates typically vary between 9 pence and 14 pence per unit.
A 100-watt lightbulb left on for 10 hours will consume 1 kilowatt hour (1 kWh or 1 unit) of electricity.
