What does watthour mean?
A watthour (Wh) is a unit of electrical energy. It equals the energy used when a power of one watt is maintained for one hour, equivalent to 3,600 joules. The term is used mainly in electricity, electronics, energy engineering, and appliance or battery specifications. Unlike a watt, which measures power or the rate at which energy is transferred, a watthour measures energy itself. Consequently, values can be added over time: a device consuming 100 watts for 10 hours uses 1,000 watthours. The unit is also used as a building block for larger units, especially the kilowatt-hour (kWh), which is common in electricity bills and grid reporting. Although the compound may be written as watthour in running text, watt-hour is also common, particularly in compound technical writing. Its value is chiefly practical: it connects an instantaneous electrical rate with an amount of energy consumed over time.
nounA unit of electrical energy equal to the energy used when a power of one watt is maintained for one hour. One watthour is equivalent to 3,600 joules.
- A unit of electrical energy equal to the energy used when a power of one watt is maintained for one hour, equivalent to 3,600 joules.
"The portable battery has a capacity of 50 watthours."
"The battery is rated at 50 watthours."
"Running a 1,500-watt heater for one hour consumes 1,500 watthours of energy."
The standard plural is watthours; one watthour is singular.
"The meter recorded 15 watthours of electricity used."
A watt says how fast energy moves; a watthour says how much energy has moved.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of watthour
Watthour is a compound formed from the units watt and hour. The watt is named after Scottish engineer James Watt, while hour derives ultimately from Latin hora. The formation follows the established method of naming a product unit by combining two unit names, a pattern also seen in kilowatt-hour.
Related word forms
How watthour is actually used
This is formal technical terminology used in electricity, electronics, energy engineering, and equipment specifications. The symbol for the unit is Wh, while kWh denotes the larger kilowatt-hour. The compound may be written as one word in running text or hyphenated as watt-hour in technical writing.
Easily confused with watthour
A watt measures power, or the rate at which energy is transferred, whereas a watthour measures an amount of energy over time.