A BTU, short for British Thermal Unit, is a standardized measurement of energy. Technically, 1 BTU is roughly equal to the amount of energy required to increase 1 pound of water 1 degree F.

In North America, the BTU is used to describe both the heat content of fuels and the power of heating and cooling appliances such as furnaces, air conditioners, water heaters, stoves, fireplaces, and barbecues. When used as this type of measurement, the term “BTU” actually refers to BTUs per hour (BTU/h).

When buying a heating or cooling appliance, be sure you understand whether the stated BTU capacity refers to the unit’s input or output. An input BTU refers to the fuel used; an output BTU measures the heat (or cooling) created.

In some cases, it’s necessary to convert BTUs to another form of measurement. Here are a few helpful conversions:

• 1 BTU equals 252–253 calories
• 1 BTU equals .293071 watt hours
• 1 watt is approximately 3.41214 BTU hours
• 1,000 BTU hours equals approximately 293.071 watts
• 1 therm equals 100,000 BTUs
• 1 “ton” of cooling equals 12,000 BTUs per hour
• 1 standard cubic foot of natural gas yields 1,030 BTUs