The kilowatt-hour (kWh) equals 3,600,000 joules and is the standard billing unit for residential and commercial electricity consumption worldwide. Utility companies charge by the kilowatt-hour, and understanding this unit helps consumers evaluate appliance running costs and solar panel output. One kilowatt-hour represents the energy used by a 1,000-watt appliance running for one hour.

The watt-hour (Wh) equals 3,600 joules, representing the energy consumed by a one-watt device operating for one hour. It is commonly used for small battery capacities, solar panel output ratings, and electric vehicle charging metrics where kilowatt-hours would be too large a unit. One watt-hour equals exactly 0.001 kilowatt-hours or about 3.412 BTU.