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Engineering ToolBox > Units of Heat - BTU, Calorie and Joule

The most common units of heat are BTU - British Thermal Unit, Calorie and Joule

The most common units for heat are

• BTU - British Thermal Unit
• Calorie
• Joule

BTU - British Thermal Unit

The unit of heat in the imperial system - the BTU - is

• the amount of heat required to raise the temperature of one pound of water through 1^oF (58.5^oF - 59.5^oF) at sea level (30 inches of mercury).
• 1 Btu (British thermal unit) = 1055.06 J = 107.6 kpm = 2.931 10^-4 kWh = 0.252 kcal = 778.16 ft.lbf = 1.05510¹⁰ ergs = 252 cal = 0.293 watt-hours

An item using one kilowatt-hour of electricity will generate 3412 BTU.

Calorie

A calorie is

• the amount of heat required to raise the temperature of one gram of water 1^oC.
• 1 kcal = 4186.8 J = 426.9 kp.m = 1.163 10^-3 kWh = 3.088 ft.lbf = 3.9683 Btu = 1000 cal

The calorie is outdated and commonly replaced by the SI-unit Joule.

Joule

The unit of heat in the SI-system the Joule is

• the mechanical energy which must be expended to raise the temperature of a unit weight (2 kg) of water from 0^oC to 1^oC, or from 32^oF to 33.8^oF.
• 1 J (Joule) = 0.1020 kpm = 2.778 10^-7 kWh = 2.389 10^-4 kcal = 0.7376 ft.lbf = 1 kg.m²/s² = 1 watt second = 1 Nm = 1 ft.lb = 9.478 10^-4 Btu

• Converting between heat and energy units