By Zencalcy Editorial TeamLast reviewed About us
A rocket generates thrust by throwing mass backwards and by the pressure difference across its nozzle. The momentum term is the mass flow times the effective exhaust velocity; the pressure term is the exit area times the difference between exit and ambient pressure. In vacuum the pressure term helps; at sea level with a correctly expanded nozzle it is near zero.
Thrust from exhaust mass flow, velocity and nozzle pressure.
F = ṁ v_e + (p_e − p₀) A_e
ṁ is mass flow, v_e is effective exhaust velocity, p_e is nozzle exit pressure, p₀ is ambient pressure and A_e is exit area. Effective exhaust velocity already accounts for any pressure contribution in the rated specific impulse.
| Symbol | Meaning |
|---|---|
| F | Total thrust, in newtons. |
| ṁ | Propellant mass flow rate, in kg/s. |
| v_e | Effective exhaust velocity, in m/s. |
| p_e − p₀ | Nozzle exit pressure minus ambient pressure, in Pa. |
| A_e | Nozzle exit area, in m². |
With 10 kg/s and 3,000 m/s the momentum thrust is 30,000 N. If exit and ambient pressure are equal the pressure term vanishes, so total thrust is 30 kN — about 3.06 tonnes-force.
Continue with the Weight Calculator, Apparent Weight in an Elevator, or the Banked Turn Calculator — or browse more dynamics tools and all physics calculators.
No. Thrust comes from conservation of momentum: the engine throws exhaust backward, so the vehicle is pushed forward. Rockets produce more thrust in vacuum, not less, because there is no ambient pressure opposing the nozzle.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Content updated: September 2026