Mean Effective Pressure

The mean effective pressure is related to the operation of a reciprocating engine and is a valuable measure of an engine's capacity to do work which is independent of the amount of engine displacement.

Mean effective pressure is another way to measure the engine performance. The cylinder pressure varies palpably while the gas expands during the power stroke in an engine. Peak pressure is available just after TDC, but pressure drops readily as the piston moves towards BDC. While signifying the cylinder pressure, it is helpful to refer to the average or mean effective pressure throughout the whole power stroke.


T = torque in newton-metre
nc = number of revolutions per power stroke (for a 4-stroke engine nc =2)
Vd = displacement volume in cubic metre
The units used for mean effective pressure may be either kilo Newton / square meter (kN/m2) or bars (where: 1 bar ¼ 100 kN/m2).