# What is the combustion efficiency of liquid fuel rockets?

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1. May 9, 2018

### Cato

How efficiently is the fuel burned in a typical liquid fuel rocket engine? I've heard numbers ranging from 95% to below 50%.

2. May 9, 2018

### Staff: Mentor

This is not a direct answer to your question. However, it indicates that combustion efficiency is not the right question.

3. May 10, 2018

### cjl

As anorlunda indicates, combustion efficiency really isn't the correct figure of merit. Instead, rocket engineers look at things like impulse density (how much momentum change can you get from a given volume of fuel), specific impulse (how much momentum change can you get from a given mass of fuel), and thrust per engine diameter (different fuels will require different sizes of engines to produce the same thrust).