Specific Impulse Calculator Formula

Understand the math behind the specific impulse calculator. Each variable explained with a worked example.

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Formulas Used

Specific Impulse

isp = exhaust_velocity / 9.80665

Thrust per Flow Rate

thrust_per_flow = exhaust_velocity

Variables

VariableDescriptionDefault
exhaust_velocityExhaust Velocity(m/s)3000

How It Works

Specific Impulse

Specific impulse (Isp) measures rocket engine efficiency: how much thrust per unit weight of propellant consumed per second.

Formula

Isp = ve / g0

  • *ve* = effective exhaust velocity (m/s)
  • *g0* = 9.80665 m/s2 (standard gravity)

    • Higher Isp means more efficient use of propellant. Chemical engines: 200-450 s. Ion engines: 1500-5000 s.

    Worked Example

    Engine with exhaust velocity 3000 m/s.

    exhaust_velocity = 3000
    1. 01Isp = ve / g0
    2. 02Isp = 3000 / 9.80665
    3. 03Isp = 305.9 s

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