Combustion ratio is the amount of reactants reacted powering the pump divided by the amount of reactants powering the pump. A value of zero means that the pump is powered only by evaporated reactants. A value of one means that the pump is powered only by reacted reactants, as when spinning the rocket engines around a pivot and pressurizing the reactants with centrifugal force.

Evaporation engines are quite reliable; but, generally less powerful than pumps powered by combustion products. For internal combustion pumps, since the reaction temperature for liquid fuels is around six thousand Kelvin, generally only a part of the reactants are reacted so that the turbine can operate at a lower temperature that avaliable materials can withstand. External combustion pumps, like putting a turbine at the rear of the rocket engine or a spinning engine, tap fully combusted reactants. Combustion ratio is used along with exhaust molecular, fuel mass ratio, fuel molecular, oxidizer mass ratio, oxidizer molecular, propellant mass ratio, propellant molecular, propellant usage, pump efficiency, reactant propellant usage and working temperature to calculate the pump energy which is in turn used to calculate the pump boost.

propellant energy = propellant usage * pump efficiency * working temperature * 8,314 J * K / kmol / 0.2
 

combustion exhaust = combustion ratio / exhaust molecular

uncombustion = 1.0 - combustion ratio

pump energy = propellant energy * propellant mass ratio / propellant molecular + propellant energy * reactant propellant usage * ( fuel mass ratio * ( uncombustion / fuel molecular + combustion exhaust ) + oxidizer mass ratio * ( uncombustion / oxidizer molecular + combustion exhaust ) )

pump boost = pump energy / pump need
 
 

This is used in pumped rocket and rocket cost.
 
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