How this calculator works
Rocket thrust combines exhaust momentum flow and the pressure difference across the nozzle exit. Use actual nozzle exit velocity here; an effective exhaust velocity may already contain pressure thrust and must not have it counted twice. Mass-flow mode uses kg/s. Burn mode obtains the rate from consumed propellant divided by burn duration and assumes a constant average rate.
Formula
F = mdot ve + (pe-pa)Ae; mdot = mburn/t. Rearrange for one unknown. Equal exit and ambient pressure make pressure thrust zero and leave nozzle area undetermined.
Worked example
A flow of 2 kg/s at 100 m/s supplies 200 N. An exit area of 2 m2 with exit pressure 30 Pa and ambient pressure 10 Pa adds 40 N, giving 240 N total.
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Frequently asked questions
Can pressure thrust be negative?
Yes, when exit pressure is below ambient. The simple expression does not model flow separation inside an overexpanded nozzle.
Are the pressures absolute?
Yes. Use absolute exit and ambient pressures consistently.
Is mass loss rate measured in kilograms?
It is kilograms per second. A total burned mass must be divided by its burn time.