British thermal unit
noun
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Despite its name, the British thermal unit, or BTU, may be more widely used in North America than in Britain. Air conditioners, furnaces, and stoves are generally rated by BTUs. (Though "BTUs" is often short for "BTUs per hour;" in air-conditioner ratings, for instance, "BTUs" really means "BTUs of cooling capacity per hour".) Fuels such as natural gas and propane are also compared using BTUs. The BTU first appeared in 1865 and isn't part of the metric system—the metric unit of energy is the much smaller joule—so it isn't much used by scientists, but its practicality keeps it popular for consumer goods and fuels. A better-known heat unit is the calorie; a BTU is equal to about 252 calories. (Since the familiar food calorie is actually a kilocalorie, a BTU equals only about a quarter of a food calorie.)
Examples of British thermal unit in a Sentence
Mary Cunningham, CBS News, 4 Feb. 2026
Meanwhile, natural gas prices surged again this morning on the bitter cold, topping $6 per million British thermal units for the first time since late 2022.
—Jim Cramer, CNBC, 26 Jan. 2026
Prices spiked more than 60% in just a few days, jumping from around $3 per million British thermal units to above $5, as expectations of surging heating demand collided with fears of supply disruptions.
—Benzinga, Freep.com, 24 Jan. 2026
That refers to a 1993 House vote on a controversial energy tax during the first year of Bill Clinton's presidency based on British thermal units.
—Bart Jansen, USA Today, 8 June 2025
What to look for in a quality Char-Broil grill
BTU
British thermal units are a measure of heat performance that applies to gas grills.
—Bestreviews, Chicago Tribune, 23 May 2025
According to the Energy Information Administration, renewables provided about 9%, or 8.2 quadrillion British thermal units, of total U.S. energy consumption in 2023.
—Kurt Snibbe, Oc Register, 22 Apr. 2025
It’s measured in square inches and British thermal units, which relate to the amount of heat the grill can produce.
—Bestreviews, Mercury News, 3 Apr. 2025
Cite this Entry
“British thermal unit.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/British%20thermal%20unit. Accessed 15 Feb. 2026.
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