Megajoule to British Thermal Units
MJ
BTU
Conversion History
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Quick Reference Table (Megajoule to British Thermal Units)
| Megajoule (MJ) | British Thermal Units (BTU) |
|---|---|
| 1 | 947.81712033128434588431 |
| 3.6 | 3,412.1416331926236451835 |
| 34.2 | 32,415.34551532992462924327 |
| 100 | 94,781.71203312843458843062 |
| 288 | 272,971.33065540989161468019 |
| 1,000 | 947,817.12033128434588430622 |
About Megajoule (MJ)
A megajoule (MJ) equals one million joules and is used in energy economics, vehicle fuel consumption comparisons, and industrial processes. Natural gas supply contracts and household gas meters often express energy in megajoules. The kinetic energy of a passenger car traveling at motorway speed is on the order of one megajoule. Electric vehicle battery capacities are sometimes expressed in megajoules to allow direct comparison with fossil fuel equivalents.
A 1-liter bottle of petrol contains about 34.2 MJ of chemical energy. A car traveling at 100 km/h has roughly 0.5 MJ of kinetic energy.
About British Thermal Units (BTU)
The British thermal unit (BTU) is the amount of heat required to raise one pound of water by one degree Fahrenheit at its maximum density (~39°F). One BTU equals approximately 1,055 joules. It remains the dominant unit for heating and cooling equipment in the United States — air conditioners, furnaces, heat pumps, and water heaters are all rated in BTU or BTU/hour. Natural gas prices in the US are quoted in dollars per million BTU (MMBtu).
A standard residential air conditioner is rated at 10,000–24,000 BTU/hour. Burning one kitchen match releases roughly 1 BTU of heat.
Etymology: Developed in the 19th century alongside the rise of steam engineering in Britain and the US, standardized as the energy needed to raise one pound of water by one degree Fahrenheit. The "British" name stuck even as the UK adopted SI units.
Megajoule – Frequently Asked Questions
How many megajoules of energy are in a liter of petrol?
About 34.2 MJ per liter (roughly 131 MJ per US gallon). Diesel is slightly higher at ~38.6 MJ/L. This energy density is why fossil fuels remain hard to replace — a Tesla Model 3 battery weighing 480 kg stores about 216 MJ, while 6 liters of petrol (roughly 4.5 kg) store the same energy content.
Why do natural gas bills sometimes show megajoules?
Natural gas is sold by energy content rather than volume because the heating value per cubic meter varies with gas composition. In Australia, billing is in MJ; in the UK and US, it is in therms or kWh. One cubic meter of pipeline-quality natural gas holds about 38–39 MJ. Using megajoules lets suppliers and customers compare across different gas sources fairly.
How much kinetic energy does a car have at highway speed in megajoules?
A 1,500 kg car at 110 km/h (about 30.6 m/s) carries ½ × 1500 × 30.6² ≈ 0.70 MJ of kinetic energy. Double the speed and the energy quadruples to 2.8 MJ. This is why highway crashes are so much more destructive than city collisions — and why braking distance scales with the square of speed.
What is the megajoule equivalent of a kilowatt-hour?
One kilowatt-hour equals exactly 3.6 megajoules (1,000 W × 3,600 s = 3,600,000 J). This conversion pops up constantly in energy-sector work: a power plant producing 1,000 MWh per day delivers 3,600,000 MJ. The 3.6 factor is worth memorising for anyone comparing electrical and thermal energy.
How many megajoules does the average house use per day?
A typical US home uses about 30 kWh/day of electricity (108 MJ) plus another 100–200 MJ of natural gas for heating and hot water — so roughly 200–300 MJ total. A well-insulated European passive house might get by on 50–70 MJ/day. Solar panels on a rooftop generate about 15–25 MJ per panel per day depending on location.
British Thermal Units – Frequently Asked Questions
Why are air conditioners rated in BTU instead of watts?
US HVAC manufacturers adopted BTU/hour because heating and cooling equipment historically measured heat removal or addition, not electrical input. A 12,000 BTU/h window unit removes 12,000 BTU of heat per hour from a room — that figure directly tells you the cooling capacity. Watts measure electrical power consumed, which is less due to the efficiency (EER) of the unit. The convention stuck because the entire US supply chain uses it.
How many BTU does it take to heat a room?
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.
What is the difference between BTU and BTU/h?
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.
How does the BTU relate to natural gas pricing in the US?
US natural gas is priced in dollars per million BTU (MMBtu) at the wholesale level and dollars per therm (100,000 BTU) on residential bills. One cubic foot of pipeline gas contains roughly 1,020 BTU. The Henry Hub benchmark price of $2.50/MMBtu means each therm costs about $0.25 wholesale — residential prices are higher after delivery and utility markups.
Why does the UK no longer use British thermal units despite the name?
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.