British thermal unit

\mathrm{BTU} = 1,055.05585262\ \text{J}

Value	1.05505585262 kJ (1,055.05585262 J) Use in the calculator →
Status	Exact by definition: no uncertainty
Source	5th International Conference on the Properties of Steam (1956); NIST SP 811
Categories	Thermodynamic Engineering & Trade

British thermal unit in every energy unit

Unit	Value
kilojoule	1.0550559 kJ
joule	1,055.0559 J
calorie	252.1644 cal
British thermal unit	1 BTU
inch-pound	9,338.0311 in·lb
foot-pound	778.16926 ft⋅lb
calorie (International Table)	251.99576 cal IT
BTU (thermochemical)	1.0006692 BTU th

28 more energy units

electron volt	6.5851407e+21 eV
hartree	2.4199946e+20 Eh
kiloelectron volt	6.5851407e+18 keV
megaelectron volt	6.5851407e+15 MeV
gigaelectron volt	6,585,140,700,000 GeV
nanojoule	1,055,055,900,000 nJ
erg	10,550,559,000 erg
teraelectron volt	6,585,140,700 TeV
microjoule	1,055,055,900 µJ
millijoule	1,055,055.9 mJ
watt-hour	0.29307107 Wh
kilocalorie	0.2521644 kcal
megajoule	0.0010550559 MJ
horsepower-hour	0.00039301478 hp·h
kilowatt-hour	0.00029307107 kWh
therm	0.00001 therm
gigajoule	0.0000010550559 GJ
million BTU	0.000001 MMBTU
megawatt-hour	2.9307107e-07 MWh
ton of TNT	2.5216440e-07 t TNT
tonne of oil equivalent	2.5199576e-08 toe
terajoule	1.0550559e-09 TJ
gigawatt-hour	2.9307107e-10 GWh
kiloton of TNT	2.5216440e-10 kt TNT
petajoule	1.0550559e-12 PJ
terawatt-hour	2.9307107e-13 TWh
megaton of TNT	2.5216440e-13 Mt TNT
quad	1.0000000e-15 quad

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 4 solvers

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}

Tons of Refrigeration from BTU/hr

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

Revised 16 October 2026

Cite this page

formula.expert. (2026, October 16). British thermal unit. https://formula.expert/constants/british-thermal-unit