What this calculator does
Ideal Rocket Equation works out velocity change a rocket can achieve from its exhaust velocity and the propellant mass burned. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
The inputs explained
| Field | What to enter |
|---|---|
| Initial mass (wet, with propellant) (kg) | A number, measured in kg. Starts at 50000. |
| Final mass (dry, propellant spent) (kg) | A number, measured in kg. Starts at 12000. |
| Specific impulse (s) | A number, measured in s. Starts at 311. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with initial mass (wet, with propellant)
Every other input is held at the calculator’s starting values while initial mass (wet, with propellant) varies. Select any row to load that scenario into the calculator.
| Initial mass (wet, with propellant) (kg) | Delta-v (Δv) | Delta-v (Δv) | Effective exhaust velocity |
|---|---|---|---|
| 25,000 | 2,238.5 m/s | 2.239 km/s | 3,049.9 m/s |
| 37,500 | 3,475.1 m/s | 3.475 km/s | 3,049.9 m/s |
| 50,000 | 4,352.5 m/s | 4.353 km/s | 3,049.9 m/s |
| 75,000 | 5,589.1 m/s | 5.589 km/s | 3,049.9 m/s |
| 100,000 | 6,466.5 m/s | 6.467 km/s | 3,049.9 m/s |
| 150,000 | 7,703.1 m/s | 7.703 km/s | 3,049.9 m/s |