British thermal unit
| Value | 1,055.05585262 J |
| Status | Exact by definition — no uncertainty |
| Source | 5th International Conference on the Properties of Steam (1956); NIST SP 811 |
| Categories | ThermodynamicEngineering & Trade |
British thermal unit in every energy unit
| 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 |
| inch-pound | 9,338.0311 in·lb |
| joule | 1,055.0559 J |
| foot-pound | 778.16926 ft⋅lb |
| calorie | 252.1644 cal |
| calorie (International Table) | 251.99576 cal IT |
| kilojoule | 1.0550559 kJ |
| BTU (thermochemical) | 1.0006692 BTU th |
| British thermal unit | 1 BTU |
| 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.