British thermal unit

\mathrm{BTU} = 1055.05585262\ \text{J}

Value	1055.05585262 J
Status	Exact by definition — no uncertainty
Source	5th International Conference on the Properties of Steam (1956); NIST SP 811
Categories	Thermodynamic Engineering & Trade

BTU in every energy unit

joule	1,055.0559 J
kilojoule	1.0550559 kJ
megajoule	0.0010550559 MJ
calorie	252.1644 cal
kilocalorie	0.2521644 kcal
watt-hour	0.29307107 Wh
kilowatt-hour	0.00029307107 kWh
British thermal unit	1 BTU
foot-pound	778.16926 ft⋅lb
electron volt	6.5851407e+21 eV
kiloelectron volt	6.5851407e+18 keV
megaelectron volt	6.5851407e+15 MeV

Learning zone

The BTU is the imperial cousin of the calorie: the heat that raises one pound of water one Fahrenheit degree, which works out to 1055.06 J. Like the calorie it comes in variants — the thermochemical BTU is 1054.35 J, the 39 °F BTU is 1059.67 J — and like the calorie the ambiguity was settled by definition, with the international-table BTU fixed at exactly 1055.055 852 62 J in 1956.

It dominates North American HVAC and gas metering, almost always as a rate: BTU per hour. Useful anchors are 3412 BTU/h per kilowatt, 12 000 BTU/h per ton of refrigeration, and roughly 100 000 BTU per therm of natural gas. One BTU is about the heat from a single kitchen match, which makes the scale of a 100 000 BTU/h furnace vivid.

Used by these solvers

Tons of Refrigeration from BTU/hr

T = \frac{\dot{Q}}{12{,}000\ \text{BTU/hr}}

Air Sensible Heat (1.08 Rule)

\dot{Q}_s = \rho_a c_a \dot{V} \, \Delta T

Boiler Horsepower to Heat Output

Q = 33{,}475 \; \text{BHP}

Seasonal Heating Energy (Degree-Day Method)

E = \frac{\dot{Q}_d \, \Delta T_m \, t}{\Delta T_d \, \eta}