Rocket Fuel Mass Calculator
How much propellant a rocket needs to deliver a given change in velocity, from its dry mass and engine efficiency — the Tsiolkovsky rocket equation, which is why rockets are almost all fuel.
The rocket equation says delta-v equals exhaust velocity times the natural log of the mass ratio: full mass over empty mass.
How the rocket fuel mass calculator works
The rocket equation says delta-v equals exhaust velocity times the natural log of the mass ratio: full mass over empty mass. Turn it around and the propellant needed grows exponentially with delta-v. Reaching orbit needs about 9.4 km/s; with a good kerosene engine at 350 s that is a mass ratio near 16 — the rocket is 94% propellant.
That exponential is why every extra kilogram of payload costs many kilograms of fuel, why staging exists, and why a small gain in specific impulse is worth a large gain in structure.
Formula: Δv = vₑ ln(m₀ / m₁); propellant = m₁ (e^(Δv / vₑ) − 1), vₑ = Isp × g₀
Worked examples
| Inputs | Propellant required (kg) | Note |
|---|---|---|
| To orbit on kerosene | 72,332 | 94% propellant |
| A hydrogen upper stage | 7,377 | a far easier ratio |
| A Mars insertion burn | 932 | a third propellant |
FAQFrequently asked questions
What is the rocket equation?
Tsiolkovsky's 1903 result: delta-v equals exhaust velocity times the log of the mass ratio. It is exact for a rocket in free space and the starting point of every mission design.
Why are rockets mostly fuel?
Because the propellant needed grows exponentially with delta-v. Orbit needs about 9.4 km/s including losses; at 3.4 km/s exhaust velocity that is a mass ratio of 16.
What is specific impulse?
Exhaust velocity divided by standard gravity, in seconds. Kerosene engines reach about 300 to 350, hydrogen 450, ion drives 3,000 or more.
Why does staging help?
Dropping empty tanks part-way means the later burns are not accelerating dead mass. Two stages can reach a total delta-v no single stage of the same technology could.
Does this include gravity and drag losses?
Only if they are in the delta-v you enter. A launch to low orbit is about 7.8 km/s of orbital speed plus 1.5 to 2 km/s of losses, which is where 9.4 comes from.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G and the speed of light
- IAU 2015 Resolution B3 — nominal solar and planetary conversion constants — the astronomical unit, solar mass and planetary radii
- NASA — the US space agency
Last checked: September 2026. Constants are CODATA 2018 (G, c) and IAU 2015 nominal values (solar and planetary parameters).