🌍 Earth Orbital Speed Calculator
Enter a planet’s average orbital radius and orbital period to calculate its average orbital speed around the Sun. Defaults to Earth’s own values.
How fast does a planet orbit?
A planet’s orbital speed depends on how far it is from the Sun and how long it takes to complete one orbit. Earth’s default values here give its well-known average orbital speed of roughly 29.8 km/s.
The formula
For a circular approximation of an orbit, average orbital speed is v = (2π × r) ÷ T, where r is the orbital radius (converted from astronomical units to meters, 1 AU = 1.495978707 × 1011 m) and T is the orbital period converted to seconds.
Real planetary orbits are elliptical, not circular, so actual instantaneous speed varies throughout the orbit, faster at perihelion (closest to the Sun) and slower at aphelion (farthest), per Kepler’s second law. This calculator gives the average speed over a full orbit, for general astronomy education.