Free · Physics models
Ideal Rocket Velocity Change
Estimate ideal velocity change from exhaust speed or specific impulse and a positive mass ratio.
- Formula & worked example
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
Delta-v (Δv) = 693.14718. The worked example lists its inputs and unit conventions.
Δv = ve ln(mi/mf); impulse branch ve = 9.81 Isp.
Worked example
Enter these known values and leave the other values blank.
- I want to input
- 1
- Exhaust velocity (vₑ)
- 1 km/s
- Initial mass (m₀)
- 100 kg
- Final mass (mₜ)
- 50 kg
- Delta-v (Δv)
- 693.1 m/s
Assumptions and limitations
- Masses include the complete vehicle before and after propellant consumption and must satisfy mi ≥ mf > 0. Exhaust speed is constant. Gravity, aerodynamic and steering losses are omitted. The impulse branch deliberately retains rounded g = 9.81 m/s².
- Clear the quantity to solve an inverse; keep known quantities fixed with locks. Some inverses are singular or ambiguous and require further known values.
- Unit selectors convert the same physical quantity. Rounded reference constants and presets limit physical accuracy even when arithmetic displays more digits.
Common questions
What does this model assume?
Masses include the complete vehicle before and after propellant consumption and must satisfy mi ≥ mf > 0. Exhaust speed is constant. Gravity, aerodynamic and steering losses are omitted. The impulse branch deliberately retains rounded g = 9.81 m/s².
Can I solve for an input?
Editable calculated fields support the captured inverse relationships. Clear the unknown and supply enough independent known values; an inverse must remain within the declared physical domain.
References
Enforce the reviewed model domain: Final mass must be positive. Initial mass must be at least the final mass.