• D is the Orbital Distance (AU)
• P is the period of orbit (years) 

Orbital distance is used to determinate how long it takes for an object to revolve around another one. The SI unit of orbital distance is AU. For example, planets revolving around sun, moon revolving around earth etc. 

This formulation was discovered by Johannes Keppler, and is known as Kepler's Third Law of Motion. 

P² = D³

According to the law, the squares of the orbital periods of the planets are directly proportional to the cubes of the semi-major axes of their orbits. Kepler's Third Law implies that the period for a planet to orbit the Sun increases rapidly with the radius of its orbit.

For Example:

Consider Period of years, P = 5 years

Then the orbital distance, D  =  (P²)^1/3

     = (5²)^1/3

     = 2.92401774 AU