The British Thermal Unit (BTU) is the **252 calories of heat** needed to raise a pound of water’s temperature by one degree Fahrenheit. British thermal units (BTU) are a unit used to measure the amount of heat in fuels or other energy sources. The amount of heat needed to raise a pound of liquid water’s temperature by one degree Fahrenheit at the point where water has its highest density (approximately 39 degrees Fahrenheit).

When compared to the energy consumption of a single household or a whole nation, **one BTU is incredibly little**. The US utilized roughly 97.33 quadrillion BTU of energy in 2021. One quadrillion is expressed as a 1 followed by 15 zeros, or 1,000,000,000,000,000.

It is possible to compare energy sources or fuels on an equal footing using their energy or heat contents. Fuels can be measured in terms of their energy or heat content rather than in physical units of measurement like weight or volume. As a measure of energy content, the U.S. Energy Information Administration (EIA) employs BTU.

**History of British Thermal Unit**

Since 1956, the British thermal unit (BTU), a unit used to quantify the amount of heat, has been defined as roughly equal to 1,055 joules, or 252 grams of calories. Previously, it was described as the amount of heat needed to increase a pound of water’s temperature by one degree Fahrenheit. Because it was reliant on the water’s starting temperature, the definition was altered. The therm, or 100,000 BTU, is a greater unit of measurement for **gas consumption** that is widely used by gas utilities.

Another heat measurement unit used in the US is the BTU. The amount of heat needed to increase 1 lb of water’s temperature by 1°F is equal to 1 BTU. The rate at which heat (or cooling) can be transferred (or extracted) by these devices within living and working spaces is measured in thousands or tens of thousands BTU/h in the United States. Examples of domestic and commercial heating and cooling systems include water heaters, boilers, furnaces, air conditioners, and heat pumps.

**Also Read:** What is Ambient Temperature?

**Use of British Thermal Unit**

A common quantity for measuring thermal energy is the British thermal unit (BTU). The energy needed to raise one pound (avoirdupois) of water’s temperature by one degree Fahrenheit is equal to one BTU (F). Mostly used in the United States and occasionally in the United Kingdom, the **BTU is a non-metric unit of energy** (UK). The joule (J), a unit of energy based on the international system of units, is utilised by numerous other nations (SI).

A BTU is approximately 1055 joules (or 1055 watt-seconds). The BTU is used in computers to gauge the output of heat-generating equipment. BTUs per hour (BTU/h) are the units used to express heat output. It takes 3.7 BTU/h to dissipate one watt of heat.