Millijoule

Millijoule (symbol mJ) is the SI unit of energy equal to one thousandth of a joule. The prefix milli denotes 10^-3, so 1 mJ = 10^-3 J. Since the joule is also equivalent to one watt-second, 1 mJ equals 1e-3 watt-seconds as well.

Millijoules are used to express relatively small amounts of energy in science and engineering. They commonly appear in descriptions of short laser pulses, energy transferred in small actuators, and the energy stored in compact capacitors or energy-harvesting devices. In laboratory settings, mJ is a convenient scale between microjoules and joules for quantities that are too large for microjoules but too small for joules.

Conversions and related units include: 1 J = 1000 mJ, so 1 mJ = 0.001 J. More prefixes scale accordingly: 1 mJ = 1000 μJ and 1 μJ = 1000 nJ. For context with other energy scales, 1 eV ≈ 1.602 × 10^-19 J, so 1 mJ corresponds to about 6.24 × 10^15 eV. While electronvolts are common in particle physics, millijoules are typically used for macroscopic energy measurements in laboratory and engineering contexts.