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 BTU (British Thermal Unit) equals approximately 1,055.06 joules, defined as the heat needed to raise one pound of water by one degree Fahrenheit. It is the primary unit for rating heating and cooling equipment in the United States, appearing on air conditioner specifications, furnace ratings, and energy efficiency labels. One BTU equals about 0.2931 watt-hours or roughly 0.252 kilocalories.