Efficiency ratio
All machines experience losses. Therefore, you have to put in more energy than comes out of them. These losses are for various reasons and they are dissipated in the form of heat. The quotient P2 : P1 yields the efficiency ratio h.
h (%) = P2 (W)/P1 (W) x 100%
The efficiency ratio of power tools lies between 50 and 75 percent.
(h= small Greek letter Eta)
(See also Power input, Power output, Total efficiency)