what is a megajoule?
âºâº Definition: Megajoule. The SI prefix mega represents a factor of 106, or in exponential notation, 1E6. So 1 megajoule = 106 joules. The joule (symbol J, also called newton meter, watt second, or coulomb volt) is the SI unit of energy and work. The unit is pronounced to rhyme with tool, and is named in honor of the physicist James Prescott Joule (1818-1889).