The engine pressure ratio (EPR) is the total pressure ratio across a jet engine, measured as the ratio of the total pressure at the exit of the propelling nozzle divided by the total pressure at the entry to the compressor.
Jet engines use either EPR or compressor/fan RPM as an indicator of thrust. When EPR is used, the pressures are measured in front of the compressor and behind the turbine.
The integrated engine pressure ratio (IEPR) is the ratio of the pressure at the core engine exhaust and fan discharge pressure compared to the intake pressure to the gas turbine engine. The IEPR is an engine indicator system unique to the Rolls-Royce RB211.