Escape Speed Calculator
Estimate the minimum speed needed to escape a planet or moon without additional propulsion (ignoring atmospheric drag and rotation).
where G is the gravitational constant, M is mass, and r is distance from center.
What Is Escape Speed?
Escape speed (often called escape velocity) is the minimum speed an object needs to break free from a body's gravity without any further thrust. If you launch slower than this speed and do not fire engines again, gravity eventually pulls you back. If you launch at or above this speed, you can coast away forever in an idealized physics model.
For Earth, this value is about 11.2 km/s (roughly 25,000 mph), assuming launch from sea level and ignoring air resistance. Real missions are more complex, but this gives the core physical threshold.
The Escape Speed Formula
Core equation
The calculator uses:
v = √(2GM / r)
- v = escape speed (m/s)
- G = gravitational constant (6.67430 × 10-11 m3 kg-1 s-2)
- M = mass of the planet or body (kg)
- r = distance from the center of mass (m)
Important insight
The escaping object's mass does not appear in the final equation. A tiny probe and a heavy spacecraft need the same escape speed from the same starting radius. The heavy craft still needs much more energy overall, but the speed threshold is identical.
How to Use This Calculator
- Select a preset body (Earth, Moon, Mars, and more), or choose Custom.
- Enter mass in kilograms and radius in kilometers.
- Click Calculate Escape Speed.
- Read outputs in m/s, km/s, mph, percent of light speed, and relative to Earth.
For custom astrophysics scenarios, make sure radius is measured from the body's center, not from the surface. If you're launching from altitude, include that altitude in your radius input.
Example Results You Can Try
Earth
Mass ≈ 5.972 × 1024 kg, radius ≈ 6,371 km. Escape speed is around 11.19 km/s.
Moon
The Moon's smaller mass and radius give a much lower value: about 2.38 km/s. That's one reason lunar missions need less propellant to depart the Moon than Earth.
Jupiter
Jupiter has a very high escape speed (around 59.5 km/s) because of its enormous mass. This makes gravitational wells of giant planets much deeper.
Common Misconceptions
“Escape speed means you leave instantly.”
Not necessarily. You can still be moving slowly after a long climb, but if you started with at least escape speed (and no losses), you will not fall back.
“Escape speed is the same as orbital speed.”
No. Low circular orbital speed near Earth is about 7.8 km/s, lower than escape speed. In fact, escape speed at the same radius is √2 times circular orbital speed.
“Rockets must reach escape speed straight up.”
Real launches build horizontal speed to enter orbit first, then perform additional burns (if needed) to escape. Aerodynamics, gravity losses, and mission design all matter in practice.
Why Escape Speed Matters
- Designing interplanetary missions and departure burns
- Comparing how hard it is to leave different planets and moons
- Teaching energy conservation and gravitational potential
- Understanding atmospheres and planetary retention over geologic time
Final Note
This calculator is intentionally clean and educational. It provides idealized escape speed, not full mission delta-v. For mission planning, engineers include atmospheric drag, engine performance, staging, gravity assists, and safety margins. Still, escape speed is one of the most useful first principles in orbital mechanics—and a great way to build intuition.