Rocket Thrust Calculator

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Choose the unit system for all inputs and outputs. Internal calculation always uses SI.
Propellant mass consumed per second by the engine.
kg/s
Average velocity of exhaust gas at the nozzle exit relative to the rocket.
m/s
Cross-sectional area of the nozzle at the exit plane.
m²
Unit used for both nozzle exit pressure and ambient pressure inputs below.
Static pressure of the exhaust gas at the nozzle exit plane.
kPa
Surrounding atmospheric pressure. At sea level this is ~101.325 kPa; at altitude it falls, boosting thrust. In vacuum it is 0.
kPa
Full launch mass of the rocket (including propellant). Leave at 0 to skip thrust-to-weight ratio.
kg
Total thrust
777,975N

Resultant force produced by the engine (momentum + pressure terms)

Thrust777.97kN
Thrust174,896lbf
Momentum thrust802,150N
Pressure thrust-24,175N
Specific impulse (Isp)311s
Momentum thrust (N)802,150
Pressure thrust (N)-24,175

Engine produces 778.0 kN of thrust (802150 N momentum + -24175 N pressure).

  • Total thrust is 778.0 kN (174896 lbf), equivalent to lifting roughly 79331 kg under standard gravity.
  • Specific impulse (Isp) is 311.0 s. For reference, kerosene-LOX engines (like Merlin 1D) reach about 311 s at sea level and 340 s in vacuum; hydrogen-LOX engines can exceed 450 s.
  • Ambient pressure exceeds nozzle exit pressure by 24175 N, reducing total thrust. The nozzle is over-expanded for this altitude.

Next stepTo increase thrust, raise the mass flow rate, increase exhaust velocity (higher Isp propellant), or expand the nozzle to match exit pressure to ambient. At altitude, ambient pressure falls to zero in vacuum, removing the pressure penalty entirely.

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