(of an engine), the useful work performed by the gases in the cylinder of a piston engine per unit time; it is determined by the analysis of indicator cards made during engine tests.

The indicated power of a given engine is different under different operating conditions. The relation of indicated power to the frequency of revolution is called the speed characteristic. Indicator cards are read at various frequencies of revolution in order to plot the speed characteristic of the indicated power. The indicated power at a given frequency of revolution is determined by measuring the areas of the cards. The indicated power is partially consumed in overcoming the frictional forces within the engine and setting the auxiliary mechanisms in motion. The indicated power may be defined as the sum of the power produced at the crankshaft (actual horsepower) and the power consumed by losses (friction horsepower).