Find circular-orbit speed v = √(GM/r) and Kepler period T = 2π √(r³/GM).
| Speed (m/s) | – |
| Period (s) | – |
Use this calculator for a circular orbit around a spherical central mass: speed is √(GM/r) and the period follows Kepler’s third law, T = 2π √(r³/GM).
r is the orbital radius from the centre, not altitude above the surface. Low Earth orbit is Earth’s radius plus about 400 km, roughly 6.77×10⁶ m, period about 90 minutes. Earth ≈ 5.97×10²⁴ kg; the Sun ≈ 1.99×10³⁰ kg. Ellipses, drag, and J2 are ignored.
Central mass (kg): Mass of the body being orbited, in kilograms.
Radius (m): Centre-to-satellite distance in metres, not height above ground.
Speed (m/s): Circular orbital speed.
Period (s): Time for one revolution, in seconds.
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