Delta-V Calculator
Rocket Parameters
Seconds (s). Typical chemical: 250–465 s; ion: 1,000–10,000 s
Total mass including all propellant
Mass after all propellant is consumed
Enter Rocket Parameters
Select a solve mode, choose an engine preset or enter your Isp, and provide the masses to calculate delta-V and see the mass breakdown charts.
How to Use the Delta-V Calculator
Choose What to Solve For
Select your solve mode from the dropdown: 'Delta-V' is the most common — it calculates how fast your rocket can go given its propellant. Use 'Initial Mass' to find how much propellant you need, 'Final Mass' to find remaining mass, or 'Isp' to determine the engine efficiency required for a target Δv.
Select an Engine or Enter Isp
Choose from 14 real rocket engine presets — from the Merlin 1D (282 s sea level) to the NEXT-C ion thruster (4,190 s). Each preset auto-fills the specific impulse field. Alternatively, toggle to 'Exhaust Velocity' mode and enter the effective exhaust velocity in m/s directly. Isp and exhaust velocity are related by: vₑ = Isp × 9.80665 m/s².
Enter Masses and Add Stages
Enter the initial (wet) mass — the rocket fully fueled — and the final (dry) mass — after all propellant is burned. Masses can be entered in kg, metric tonnes, or pounds. For multi-stage rockets, click 'Add Stage' to add up to 3 stages, each with their own engine and masses. The total Δv will be the sum of all stage contributions.
Compare Against Mission Requirements
Use the mission preset dropdown to select your target destination (LEO, Moon, Mars, etc.). The tool shows how your rocket's Δv compares to the mission requirement with a progress bar and margin indicator. Expand the Delta-V Budget Reference Table at the bottom for a full reference of solar system mission requirements.
Frequently Asked Questions
What is specific impulse (Isp) and why does it matter?
Specific impulse (Isp) is a measure of rocket engine fuel efficiency, expressed in seconds. It represents how much thrust you get per unit weight of propellant per second. A higher Isp means your engine extracts more Δv from each kilogram of propellant. For example, a hydrogen/oxygen engine like the RS-25 has an Isp of 452 seconds in vacuum — meaning each kilogram of propellant burned produces 452 seconds worth of thrust at 1g. Compare this to a kerosene engine at 310 s: the hydrogen engine is about 46% more efficient. Ion thrusters reach 4,000+ seconds but produce such low thrust they are only practical in the vacuum of deep space. Isp determines the mass ratio needed for any given Δv, which directly affects how heavy and expensive a rocket must be.
Why do rockets need multiple stages to reach orbit?
Reaching low Earth orbit requires approximately 9,500 m/s of Δv including gravity and drag losses. With a typical kerosene/oxygen engine (Isp ~310 s), the Tsiolkovsky equation requires a mass ratio of about 21:1 — meaning 95% of the rocket's mass must be propellant. This is impossible with a single stage because you also need tanks, engines, structure, and payload. Multi-staging solves this by discarding the heavy, empty first stage once its fuel is spent. The second stage starts with a fresh mass ratio calculated only from its own full mass, not the entire launch vehicle. The Saturn V used three stages; the Falcon 9 uses two. Even with staging, rockets are predominantly propellant: a Falcon 9 on the pad is about 94% propellant by mass.
Why does the delta-V to LEO include gravity and drag losses?
The orbital velocity of LEO is approximately 7,800 m/s. However, reaching orbit from Earth's surface requires roughly 9,300–9,500 m/s of total Δv — about 1,500–1,700 m/s more. This extra cost comes from two sources. Gravity losses occur because the rocket must fight Earth's gravity during the entire burn; while thrusting vertically, all thrust is wasted overcoming gravity rather than adding horizontal velocity. Gravity losses typically amount to 1,000–1,500 m/s. Aerodynamic drag losses add another 50–200 m/s in the lower atmosphere. The exact values depend on the rocket's thrust-to-weight ratio and trajectory design. High thrust-to-weight ratios reduce gravity losses but may increase aerodynamic losses. This calculator uses vacuum Isp; a more accurate launch simulation would use sea-level Isp for the atmospheric phase.
What is mass ratio and why does it matter so much?
The mass ratio (m₀/mf) is the ratio of a rocket's initial fueled mass to its final empty mass. Because the Tsiolkovsky equation uses the natural logarithm of the mass ratio, small improvements in mass ratio have large effects. A mass ratio of 2.72 (Euler's number) gives exactly one exhaust-velocity unit of Δv. A mass ratio of 7.39 (e²) gives two units. To triple the exhaust velocity worth of Δv, you need a mass ratio of 20.1 (e³). This exponential relationship is why spacecraft engineers are obsessed with reducing structural mass — saving 100 kg of tank wall doesn't just save 100 kg, it also lets you remove hundreds of kilograms of propellant that would have been needed to carry that structure to orbit.
How does the propellant fraction relate to mission capability?
Propellant fraction (also called mass fraction) is the fraction of total wet mass that is propellant: (m₀ − mf) / m₀. Higher propellant fractions mean more capable rockets for a given Isp. Most modern chemical rockets target propellant fractions of 85–93%. The Falcon 9 first stage has a propellant fraction of about 93%; the Space Shuttle Main Engine system was around 88%. Ion-propelled spacecraft often have propellant fractions of 50–80% because their high Isp means less propellant is needed for the same Δv. A spacecraft with a propellant fraction below 50% is generally considered mass-constrained — most of its mass is structure and payload, leaving little room for propulsion performance.
Can I use this calculator for interplanetary missions?
Yes, with caveats. The Tsiolkovsky equation correctly calculates the propulsive Δv your rocket can deliver. For interplanetary missions, you can use the mission preset dropdown or the delta-V budget reference table to find the required Δv for your destination. However, interplanetary missions often use gravity assists (swingbys of planets) to gain Δv for free, which this calculator does not model. Aerobraking at Mars or Venus can also reduce the propulsive Δv needed for orbit insertion by 900–1,000 m/s. The Δv values in this calculator's reference table represent direct transfer trajectories; actual missions with gravity assists may require significantly less. For rough feasibility checks and rocket sizing, this calculator provides excellent results.