Kepler's Third Law states that the squares of the orbital periods of planets are directly proportional to the cubes of the semi-major axis of the orbits.

G = Universal Gravitational Constant = 6.6726 x 10^{-11}N-m^{2}/kg^{2}
r = Satellite Mean Orbital Radius
M = Planet Mass

The period of the Moon is approximately 27.2 days (2.35x10^{6} s). Determine the radius of the Moon's orbit. Mass of the earth = 5.98x10^{24} kg, T = 2.35x10^{6} s, G = 6.6726 x 10^{-11}N-m^{2}/kg^{2}.

Substitute the values in the below Satellite Mean Orbital Radius equation:

This example will guide you to calculate the Satellite Mean Orbital Radius manually.

Determine lo's mass, which orbits Jupiter at an orbital radius of 4.218 x 10^{8} at every 151200 seconds.
r = 4.218 x 10^{8} m, T = 151200 s, G = 6.6726 x 10^{-11}N-m^{2}/kg^{2}.

Substitute the values in the below Mass equation:

This example will guide you to calculate the Mass of the object manually.

This tutorial will help you dynamically to find the Planetary Motion of Kepler's Third Law problems.