The mass flow rate through the nozzle of a rocket engine is the amount of propellant expelled per unit of time, and it is a crucial parameter in understanding the engine’s performance.
The mass flow rate through a convergent-divergent nozzle is the quantity of fluid passing through the nozzle per unit time. This nozzle design is particularly important for achieving supersonic flow, where the nozzle consists of a converging section followed by a diverging section. The converging part accelerates the flow to sonic speed, and the diverging section continues the acceleration to supersonic speeds.
The density () for an ideal gas is given by the ideal gas law: 
which gives,
where,
- ṁ is the nozzle mass flow rate
- P is the pressure
- R is the gas constant for the working fluid
- T is the Temperature
- A is the nozzle throat are
- V is the velocity of the flow in terms of the local speed of sound