Power-to-weight ratio (or
specific power or
power-to-mass ratio) is a calculation commonly applied to
engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power source. It is also used as a measurement of performance of a
vehicle as a whole, with the
engine's power output being divided by the weight (or
mass) of the vehicle, to give a metric that is independent of the vehicle's size. Power-to-weight is often quoted by manufacturers at the peak value, but the actual value may vary in use and variations will affect performance.