Units of Heat - BTU, Calorie and Joule

Convert between common heat units: BTU (British Thermal Unit), Calorie, and Joule. Understand the definitions and relationships between these fundamental heat measurement units in imperial and SI systems.

Units of Heat - BTU, Calorie and Joule

The most common units for heat are:

  • BTU (Btu) - British Thermal Unit - the amount of heat required to raise the temperature of one pound of water through 1 °F
  • Calorie - the amount of heat required to raise the temperature of one gram of water 1 °C
  • Joule - the SI unit of energy, equal to the work done when a force of one newton acts through a distance of one meter

Conversion Factors

  • 1 Btu = 1055.06 J = 252 cal = 0.293 watt-hours
  • 1 kcal = 4186.8 J = 3.9683 Btu = 1000 cal
  • 1 J = 0.7376 ft·lbf = 9.478×10⁻⁴ Btu = 2.389×10⁻⁴ kcal
Calculator

Inputs

Results

BTU-- Btu
Calorie-- cal
Kilocalorie-- kcal
Joule-- J

Key Definitions

BTU - British Thermal Unit

The unit of heat in the imperial system. One BTU is the amount of heat required to raise the temperature of one pound of water through 1 °F (58.5 °F to 59.5 °F) at sea level.

Conversions:

  • 1 Btu = 1055.06 J
  • 1 Btu = 0.252 kcal
  • 1 Btu = 252 cal
  • 1 Btu = 778.16 ft·lbf

Calorie

Commonly defined as the amount of heat required to raise the temperature of one gram of water by 1 °C. The kilogram calorie (kcal) is used for food energy content.

Conversions:

  • 1 kcal = 4186.8 J
  • 1 kcal = 3.9683 Btu
  • 1 kcal = 1000 cal

Joule

The SI unit of heat and energy. One Joule is the work done when a force of one newton acts through a distance of one meter. 4.184 joules of heat energy is required to raise the temperature of 1 gram of water by 1 °C.

Conversions:

  • 1 J = 0.7376 ft·lbf
  • 1 J = 9.478×10⁻⁴ Btu
  • 1 J = 2.389×10⁻⁴ kcal