Convert British Thermal Unit to Joule (BTU → J)

Converting BTU to joules is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in BTU

   Start with the number of BTU (BTU) you want to convert.
2. 2
   Multiply by 1,055.0558

   The conversion factor from BTU to J is 1,055.0558. Multiply your value by this number.
3. 3
   Read the result in joules

   The result is your value in joules (J).

Multiply the value in BTU by 1,055.0558. For the reverse direction, multiply by 0.000948.

• ✓1 BTU = 1055.06 J = 0.293 Wh.
• ✓BTU/h (power) and BTU (energy) are different — don't confuse.
• ✓Tons of refrigeration: 12,000 BTU/h = 1 ton AC.

• ✗Confusing BTU and BTU/h — energy vs power.
• ✗Using kcal when BTU is requested in HVAC specs.
• ✗Treating all BTUs as exact — definitions vary (IT, thermochemical, etc.).

What is the British Thermal Unit?

The British thermal unit (BTU) equals approximately 1,055.06 joules and is the standard unit in American HVAC, gas appliances, and air-conditioner ratings. Originally defined as the heat needed to raise 1 pound of water by 1°F, the BTU is the imperial counterpart to the calorie. American gas utilities measure delivered heat in BTUs or therms (1 therm = 100,000 BTU), and air conditioners are rated by their cooling capacity in BTU per hour (a typical window AC is 5,000–12,000 BTU/h, central AC for a medium home is 24,000–60,000 BTU/h). Furnaces are similarly rated. The BTU relates to the joule (1 BTU ≈ 1,055 J), the calorie (1 BTU ≈ 252 cal), the watt-hour (1 BTU ≈ 0.293 Wh), and the therm (100,000 BTU = 1 therm). Outside the United States, the BTU is rare; metric countries use kilojoules or kilowatt-hours for the same applications.

• US air-conditioner sizing
• US heating-system capacity
• Natural gas billing in some US regions

What is the Joule?

The joule is the SI unit of energy, work, and heat, named after English physicist James Prescott Joule (1818–1889). Defined as the energy transferred when a force of one newton acts over a distance of one meter (1 J = 1 N·m), the joule unifies mechanical work, electrical energy (1 J = 1 watt-second = 1 V·C), and thermal energy. A typical apple has about 250,000 joules of chemical energy when metabolized, lifting an apple 1 meter requires roughly 1 joule of mechanical work, and a single joule could light a 1-watt LED for one second. The joule is fundamental in physics, mechanical engineering, electrical engineering, and nutrition (European food labels show kilojoules). It relates to the kilojoule (1 kJ = 1,000 J), the calorie (1 cal = 4.184 J), the watt-hour (1 Wh = 3,600 J), and the BTU (1 BTU ≈ 1,055 J). Modern definitions of the kilogram and the Kelvin both reference the joule.

• Physics and engineering calculations
• Scientific nutrition measurement (European labels)
• Impact energy in engineering (Charpy test)