What is a Megajoule?

The megajoule equals 1,000,000 joules (or 1,000 kilojoules) and is used for measuring fuel energy content, large-scale electrical work, and industrial heat applications. The energy content of food and fuel is often quoted in MJ: a kilogram of gasoline contains about 46 MJ, natural gas has 38 MJ per cubic meter, and a kilogram of coal yields 24 MJ. Vehicle fuel-economy and energy-efficiency calculations use MJ to compare disparate energy sources. Industrial process heating, boiler outputs, and large machinery energy ratings are commonly given in MJ per cycle or MJ per hour. The megajoule relates to the joule (10⁶ J = 1 MJ), the kilojoule (1,000 kJ = 1 MJ), the kilowatt-hour (1 kWh = 3.6 MJ), and the BTU (1 MJ ≈ 948 BTU). For electricity-grid energy accounting, the equivalent kilowatt-hour or megawatt-hour is more common than MJ.

Visual reference for how the megajoule relates to other energy units. Each row links to the full converter for that pair.

• Fuel energy content reporting
• Natural gas billing in some countries
• Industrial energy consumption

• ✓1 MJ = 1000 kJ = 0.278 kWh.
• ✓Natural gas heat content often quoted as MJ/m³.
• ✓For fuel economy, use MJ/km or L/100km interchangeably.

• ✗Confusing MJ with MW (power).
• ✗Using MJ for electricity bills — kWh is standard.
• ✗Mixing fuel energy (MJ) with fuel volume (L) without unit conversion.