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`T = 2pisqrt( a ^3/( "M" *G))`

Enter a value for all fields

The **Orbital Period** calculator uses Kepler's Third Law to compute the period of an orbiting body based on the semi-major axis and the mass of the center body (e.g. Sun or planet).

**INSTRUCTIONS:** Choose units and enter the following:

- (
**a**) Semi-major axis - (
**M**) Mass of major body

**Orbital Period (T):** The calculator returns the period in days. However, this can be automatically converted to compatible units via the pull-down menu.

**Kepler's Third Law**, the orbital period `T` of two bodies orbiting each other in a circular or elliptic orbit is:

`T=2pisqrt(a^3/mu)`

where:

- `a` = orbit's semi-major axis in meters
- `mu` = GM, the standard gravitational parameter in m
^{3}/s^{2}- `G` = Universal Gravity Constant
- `M` = mass of the more massive object

The formula and equation are from Wikipedia (https://en.wikipedia.org/wiki/Orbital_period).