Overall Efficiency

Overall efficiency, abbreviated as \( \eta_o \)  (Greek symbol eta), a dimensionless number, is the ratio of the actual output of a system to the expected output of a system, expressed as a percentage.  In engineering, overall efficiency is used to evaluate the performance of a system by comparing the energy input to the energy output.  For example, in a heat engine, overall efficiency is the ratio of the net work done by the engine to the heat energy input from the fuel.  Overall efficiency takes into account all losses, including friction, heat transfer, and other inefficiencies in the system.  A higher overall efficiency indicates a more effective and efficient system.