mks system, system of units of measurement based on the metric system and having the meter of length, the kilogram of mass, and the second of time as its fundamental units. Other mks units include the newton of force, the joule of work or energy, and the watt of power. The units of the mks system are generally much larger and of a more practical size than the comparable units of the cgs system. The mks system provides the basis for the International System of Units (SI).