Gigajoule to British Thermal Units (IT)

In cold-climate countries, 30–60 GJ per year is common for heating and hot water. A well-insulated modern home in Germany might use 20 GJ; a drafty older home in Canada might use 100+ GJ. Australians use about 40 GJ/year on average. Each gigajoule costs roughly $8–$15 depending on local gas prices.

One tonne of coal holds roughly 24–30 GJ depending on grade. One tonne of crude oil contains about 42–44 GJ. One tonne of LNG holds roughly 54 GJ. One tonne of dry firewood stores about 16 GJ. These figures explain why oil and gas are preferred for transport — they pack more gigajoules per kilogram than solid fuels.

One gigajoule equals 277.78 kWh. At an average electricity price of $0.15/kWh, one gigajoule of electrical energy costs about $42. The same gigajoule from natural gas costs $8–15. This price gap is the main reason gas boilers remain popular for heating in countries with cheap pipeline gas.

A single-aisle jet like the Boeing 737-800 burns about 10–12 GJ per flight hour. A six-hour transatlantic flight on a wide-body aircraft can consume 300–400 GJ of jet fuel. The entire global aviation industry uses roughly 12 billion gigajoules of fuel per year — about 3% of total world energy consumption.

At 2,000 kcal/day (8.4 MJ/day), a person consumes about 3.07 GJ of food energy per year. Over 80 years, that is roughly 245 GJ — equivalent to about 6,000 liters of petrol. Your entire lifetime food energy would fit in a medium-sized fuel tanker, which is a humbling thought.

BTU/hour expresses cooling or heating power, not energy alone. A 12,000 BTU(IT)/h rating corresponds to approximately 3,517 W of thermal power. Watts can describe thermal power as well as electrical input; the two quantities must not be confused. An air conditioner's electrical input depends on its efficiency and operating conditions, rather than being the same as its cooling capacity.

A rough rule of thumb is 20 BTU per square foot of living space in a temperate climate. A 300 sq ft bedroom needs about 6,000 BTU/h; a 1,500 sq ft open-plan living area needs roughly 30,000 BTU/h. Actual requirements vary with insulation, ceiling height, climate zone, and window area. Poorly insulated older homes may need 30–40 BTU per square foot.

BTU is a unit of energy (heat); BTU/h is a unit of power (rate of heat flow). When an air conditioner is labelled "12,000 BTU," the industry shorthand actually means 12,000 BTU per hour. Technically one BTU equals about 1,055 joules of energy, while 1 BTU/h equals about 0.293 watts. The distinction matters for energy calculations but is routinely blurred in product marketing.

Natural gas energy quantities may be billed in millions of BTU (MMBtu) or therms. A therm nominally represents 100,000 BTU, but the legal U.S. and EC therm variants have their own fixed joule definitions. This converter keeps those therm variants separate; neither should be assumed to equal exactly 100,000 BTU(IT). Always check the unit convention used on the bill.

The UK metricated energy units in the 1970s–1990s, switching gas billing from therms (100,000 BTU) to kilowatt-hours and scientific work to joules. The "British" in BTU reflects 19th-century British steam engineering origins, not current usage. Today the BTU is almost exclusively an American unit, used for HVAC, gas pricing, and appliance ratings across the US.