Orbital Period Calculator (Kepler's Law)
Astronomy & SpaceCalculate a planet or object orbital period using Kepler third law, based on its average distance from the Sun.
Orbital Period
The orbital period in Earth years, using Kepler third law (T squared proportional to a cubed, in AU and years).
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Frequently Asked Questions
What is Kepler third law?
Kepler third law states that the square of a planet orbital period is proportional to the cube of its average distance from the Sun — when distance is measured in astronomical units (AU) and period in Earth years, the relationship simplifies to T equals a to the power of 1.5.
What is an astronomical unit (AU)?
An astronomical unit is the average distance between Earth and the Sun, about 149.6 million kilometers — it is a convenient reference unit for measuring distances within our solar system.
Does this formula work for any orbiting body?
This simplified version works well for objects orbiting the Sun. For moons orbiting planets or exoplanets orbiting other stars, the full version of Kepler third law also requires factoring in the central body mass.
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