What is specific impulse (Isp)?

Specific impulse is a measure of rocket engine efficiency — the thrust produced per unit of propellant consumed per second, measured in seconds. Higher Isp means more delta-v for the same propellant mass. Typical values: chemical engines 250–450 s, ion engines 1,500–10,000 s.

Delta-v (Δv) is the total change in velocity a rocket can impart to itself by burning propellant. It is the key budget for orbital maneuvers — reaching low Earth orbit needs roughly 9,400 m/s, a trans-lunar injection adds about 3,100 m/s more.

What is g₀ in the equation?

g₀ is the standard gravitational acceleration at Earth's surface: 9.80665 m/s². It appears because Isp is measured in seconds, and multiplying by g₀ converts it to an effective exhaust velocity (m/s) used in the logarithmic calculation.

Why must initial mass be greater than final mass?

The final (dry) mass must be less than the initial (wet) mass because propellant is burned during flight. If mf ≥ m₀, there is no propellant and the mass ratio ln(m₀/mf) ≤ 0, giving zero or negative delta-v — physically meaningless.

Does this account for gravity losses or drag?

No. The Tsiolkovsky equation gives ideal, vacuum delta-v with no gravity or aerodynamic losses. Real missions subtract gravity losses (~1,000–1,500 m/s for a vertical launch) and drag losses (~100–200 m/s) from this ideal figure.

Tsiolkovsky Rocket Equation Calculator

Name: Tsiolkovsky Rocket Equation Calculator
Availability: InStock
Author: Nham Vu

Enter specific impulse, initial mass, and dry mass to compute the delta-v a rocket stage can deliver.

Rocket Parameters

Δv = Isp × g₀ × ln(m₀ / mf)

Specific Impulse (Isp) seconds

Chemical: 250–450 s | Ion: 1,500–10,000 s

Initial (wet) Mass m₀

Final (dry) Mass mf

Example Engines

Enter parameters and click Calculate to see delta-v results.

Summary

Enter specific impulse, initial mass, and dry mass to compute the delta-v a rocket stage can deliver.

How it works

Enter the specific impulse (Isp) of the rocket engine in seconds.
Enter the initial (wet) mass — fully fueled rocket mass including propellant.
Enter the final (dry) mass — rocket mass after all propellant is burned.
The calculator applies Δv = Isp × g₀ × ln(m₀ / mf), where g₀ = 9.80665 m/s².
Results show delta-v in m/s and km/s, plus the mass ratio and propellant fraction.

Use cases

Estimate how much velocity change a rocket stage can achieve.
Design multi-stage rockets by chaining delta-v budgets.
Evaluate engine choices by comparing Isp and resulting delta-v.
Solve aerospace engineering homework on propulsion systems.
Check if a spacecraft has enough delta-v to reach a target orbit.
Understand the relationship between propellant fraction and performance.

Frequently Asked Questions

Last updated: 2026-07-24 · Reviewed by Nham Vu