Calculate rocket or jet thrust from mass flow and exhaust velocity, with an optional nozzle pressure term, specific impulse and thrust-to-weight ratio.

Use axial velocities in the same engine frame and equal inlet/exit mass flow. For a rocket, enter 0 for inlet velocity; do not subtract flight speed.

0 for a rocket. For a jet, enter the intake air velocity in the engine frame.

Nozzle pressure, vehicle mass and burn time
Blank means the nozzle is matched to ambient, so pressure adds no thrust.

Blank uses standard sea level, 101,325 Pa. Enter 0 for vacuum.

Needed only when exit and ambient pressure differ.

Blank omits TWR. Zero mass makes TWR undefined.

Blank omits impulse. Enter 0 for zero duration; thrust is assumed constant.

Thrust Formula

The following formula applies to a rocket using actual nozzle exit velocity relative to the rocket and zero inlet velocity. The calculator also supports the equal-inlet/exit-mass-flow approximation F = ṁ(Vₑ − Vᵢ) + (Pₑ − Pₐ)Aₑ, with axial velocities in one engine/control-volume frame. Do not subtract rocket flight speed as inlet velocity. F/(ṁg₀) is rocket specific impulse only when ṁ is total propellant flow and the rocket-frame inlet term is zero; it is not fuel-based Isp for an air-breathing engine.

T = ṁ Ve + (Pe − Pa) Ae

  • ṁ – propellant mass-flow rate (kg/s)
  • Ve – actual nozzle exit velocity relative to the rocket (m/s), not pressure-adjusted effective exhaust velocity
  • Pe – static pressure at the nozzle exit (Pa)
  • Pa – ambient (back-) pressure (Pa)
  • Ae – exit area of the nozzle (m²)

Thrust Definition

Thrust is the force produced by an engine (such as a rocket or jet) when it expels mass as exhaust. For a rocket nozzle, thrust includes both the exhaust momentum term (ṁVe) and the nozzle pressure-difference term (Pe − Pa)Ae.

Thrust Example

How to calculate thrust?

  1. First, determine the exhaust velocity.

    Use the actual nozzle exit velocity Vₑ relative to the rocket, and enter 0 for inlet velocity.

  2. Next, determine the propellant mass flow.

    Measure the propellant mass used (Δm) over a burn time (Δt), then compute ṁ = Δm/Δt.

  3. Next, determine the pressure/area terms.

    Find the nozzle exit pressure Pₑ, ambient pressure Pₐ, and nozzle exit area Aₑ (or set Pₑ = Pₐ to neglect the pressure-thrust term).

  4. Finally, calculate the thrust.

    Compute T = ṁVₑ + (Pₑ − Pₐ)Aₑ.

FAQ

What is thrust?

Thrust is the force produced by an engine when it expels mass (exhaust). For rocket nozzles, it includes both the exhaust momentum term and (when applicable) a nozzle pressure-difference term.