Circular Orbital Velocity Calculator
Use this tool to estimate orbital speed for a circular orbit around a planet, moon, or the Sun.
What this orbital velocity calculator does
This calculator computes the speed needed to maintain a circular orbit around a central body like Earth, Mars, Jupiter, the Moon, or even the Sun. Circular orbital velocity is the balance point where gravity continuously pulls the spacecraft inward while the spacecraft moves sideways fast enough to keep missing the surface.
If the speed is too low, the object falls inward. If the speed is too high, the orbit rises (or becomes non-circular). This tool gives you a practical first estimate used in mission design, satellite planning, and educational physics work.
Formula used
The calculator uses the standard circular-orbit equation:
- v = orbital velocity in meters per second (m/s)
- G = gravitational constant =
6.67430 × 10⁻¹¹ m³/(kg·s²) - M = mass of the central body in kg
- r = distance from the center of the body to the spacecraft in meters
The calculator converts your altitude and planet radius from km to meters and uses:
How to use the calculator
- Select a central body from the dropdown (or choose custom).
- Enter the mass and radius (auto-filled for presets).
- Enter orbital altitude above the surface in kilometers.
- Click Calculate to get orbital velocity, escape velocity, and orbital period.
The result includes speed in both m/s and km/s, which makes it easy to use in aerospace references and classroom work.
Worked example: low Earth orbit
ISS-like orbit at 400 km altitude
For Earth, with altitude near 400 km, circular orbital speed comes out around 7.67 km/s. That is roughly 27,600 km/h. This is why satellites in low Earth orbit circle the planet in about 90 minutes.
Even though the station is "in space," gravity is still strong there. Orbit is not zero gravity; it is continuous free-fall around Earth.
Circular orbit vs. escape velocity
Circular orbital velocity is lower than escape velocity at the same altitude. Escape velocity is:
In other words, if you are already in circular orbit and increase speed by a factor of about 1.414 (ignoring drag and burns), you transition toward escape conditions.
Common mistakes to avoid
- Mixing units: keep mass in kg and distances in km for inputs (the tool converts internally).
- Using altitude as center distance: you must include planet radius.
- Applying this to elliptical velocity at all points: this calculator is for circular orbit speed only.
- Ignoring atmosphere: at low altitudes, drag matters and real mission speed changes over time.
Typical circular orbital speeds
Quick reference values
- Earth at 200 km: about 7.79 km/s
- Earth at 400 km: about 7.67 km/s
- Moon at 100 km: about 1.63 km/s
- Mars at 400 km: about 3.36 km/s
- Jupiter at 1000 km above cloud tops: much higher due to strong gravity
FAQ
Does spacecraft mass change orbital velocity?
Not in this ideal two-body model. Orbital speed for a circular orbit depends on central body mass and orbital radius, not spacecraft mass.
Can I use this for transfer orbits?
Not directly. Transfer orbits are elliptical and require the vis-viva equation and burn planning. This tool is best for circular orbit estimates and sanity checks.
Why does higher altitude mean lower speed?
Gravitational pull weakens with distance. In higher orbits, less centripetal acceleration is needed, so orbital speed decreases.
Final note
This orbital velocity calculator is a clean, physics-based estimator for circular orbits. It is ideal for students, educators, and early-stage mission planning. For detailed mission work, include non-spherical gravity, atmospheric drag, thrust profiles, and perturbations from other bodies.