# Engine pressure ratio

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Total pressure ratio across a jet engine

The **engine pressure ratio** (**EPR**) is the total pressure ratio across a [jet engine](/source/Jet_engine), measured as the ratio of the [total pressure](/source/Total_pressure_(fluids)) at the exit of the propelling nozzle divided by the total pressure at the entry to the compressor.[1]

Jet engines use either EPR or compressor/fan RPM as an indicator of thrust.[2] When EPR is used, the pressures are measured in front of the compressor and behind the turbine.

## Integrated engine pressure ratio

The integrated engine pressure ratio (IEPR) is a ratio used on some [turbofans](/source/Turbofan) to include fan discharge total pressure and compressor inlet total pressure. If compressor inlet pressure is P0 and fan discharge total pressure is P1, then the integrated engine pressure ratio will be P1 /P0.[3]

The IEPR is an engine indicator system unique to the [Rolls-Royce RB211](/source/Rolls-Royce_RB211).

## See also

- [Jet engine performance](/source/Jet_engine_performance)

- [Turbofan](/source/Turbofan)

## References

1. **[^](#cite_ref-1)** Glenn Research Center (NASA). ["Pressure variation - EPR"](https://www.grc.nasa.gov/WWW/k-12/airplane/epr.html). Retrieved January 2, 2015.

1. **[^](#cite_ref-2)** ["Engine Pressure Ratio (EPR)"](https://web.archive.org/web/20141004201047/http://code7700.com/epr.html). *code7700.com*. Archived from [the original](http://code7700.com/epr.html) on 2014-10-04.

1. **[^](#cite_ref-3)** ["integrated engine pressure ratio"](https://aviation_dictionary.en-academic.com/3854/integrated_engine_pressure_ratio). aviation_dictionary.en-academic.com. Retrieved 2023-06-07.

- The Boeing Company *Engine thrust control system* [US Patent 4248042](https://patents.google.com/patent/US4248042) Includes [Boeing](/source/Boeing)'s discussion on EPR or IEPR being a better indicator of thrust.

## External links

- [Pressure Variation EPR - NASA Animation](https://www.grc.nasa.gov/WWW/K-12/airplane/epr.html)

v t e Jet engines and aircraft gas turbines Gas turbines and jet propulsion Types Air turborocket Pulsejet/Valveless pulsejet/Gluhareff Pressure Jet Pulse detonation engine Propfan Turbofan Turbojet Turboprop Turboshaft Ramjet Scramjet Shcramjet Rocket Rotating detonation engine Mechanical components Accessory drive Air intake Afterburner (reheat) Axial compressor Centrifugal compressor Combustor Constant speed drive Impeller Nose bullet Propelling nozzle Turbine blade Principles Aircraft engine starting Bleed air Brayton cycle Bypass ratio Compressor stall Engine pressure ratio (EPR) Flameout Jet engine performance Overall pressure ratio Propulsive efficiency Specific impulse Thrust Thrust lapse Thrust specific fuel consumption Thrust to weight ratio Variable cycle engine Windmill restart Propellers Components Propeller governor Propeller speed reduction unit Principles Autofeather Blade pitch Constant-speed Contra-rotating Counter-rotating Proprotor Scimitar Variable-pitch Engine instruments Annunciator panel Electronic centralised aircraft monitor (ECAM) Electronic flight instrument system (EFIS) Engine-indicating and crew-alerting system (EICAS) Flight data recorder Glass cockpit Engine controls Autothrottle Full Authority Digital Engine/Electronics (FADEC) Thrust lever Thrust reversal Fuel and induction systems Flame holder Jet fuel Other systems Air-start system Auxiliary power unit (APU) Bleed air system Hydraulic system Ice protection system

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Adapted from the Wikipedia article [Engine pressure ratio](https://en.wikipedia.org/wiki/Engine_pressure_ratio) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Engine_pressure_ratio?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.