# What is British Thermal Unit (unit BTU) – Energy Unit – Definition

British Thermal Unit is a traditional unit of heat. It is part of the British Imperial system of units. British Thermal Unit (unit BTU) – Energy Unit

## Energy Units

Energy is generally defined as the potential to do work or produce heat. This definition causes  the SI unit for energy is the same as the unit of work – the joule (J). Joule is a derived unit of energy and it is named in honor of James Prescott Joule and his experiments on the mechanical equivalent of heat. In more fundamental terms, 1 joule is equal to:

1 J = 1 kg.m2/s2

Since energy is a fundamental physical quantity and it is used in various physical and engineering branches, there are many energy units in physics and engineering.

## British Thermal Unit (unit: BTU)

British Thermal Unit (unit: BTU).  British Thermal Unit is a traditional unit of heat. It is part of the British Imperial system of units. It is defined to be the amount of heat that must be absorbed by a 1 one pound of water to raise its temperature by 1 °F at the temperature that water has its greatest density (approximately 39 degrees Fahrenheit). Its counterpart in the International System of Units (SI) is the calorie, which is defined as the amount of heat required to raise the temperature of one gram of water by one degree Celsius.

• 1 British Thermal Unit (BTU) = 1055 J
• 1 British Thermal Unit (BTU) = 252 calories
• 1 British Thermal Unit (BTU) = 0.000293 kWh

References:
Reactor Physics and Thermal Hydraulics:
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6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
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9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.