Orbital Period Calculator
Enter the semi-major axis a in metres and gravitational parameter μ in m³/s². The calculator applies the two-body Kepler relation and reports the period in seconds, hours, and days.
A QUICK WALKTHROUGH
How to use this tool
- Enter the ellipse semi-major axis a in metres.
- Enter the gravitational parameter μ in m³/s².
- Calculate and read the period in three time units.
Formula and source
For an ideal two-body Keplerian orbit, T = 2π√(a³/μ), where a is the ellipse semi-major axis and μ is the gravitational parameter. See NASA’s explanation of [Kepler’s laws](https://science.nasa.gov/solar-system/orbits-and-keplers-laws/).
Model limits
This calculates an ideal period from a and μ only. It does not accept instantaneous altitude, supply body data, or model perturbations, drag, or orbit propagation. Choose physically consistent inputs for the system you are studying.
Local calculation
The calculation runs in your browser. Inputs are not uploaded or stored.
GOOD TO KNOW
Common questions
What does the semi-major axis mean?
It is half the longest diameter of the ellipse, measured from the ellipse’s centre—not an instantaneous height above a surface.
What is μ?
It is the gravitational parameter for the central body and has units of m³/s². Supply a value appropriate to your system.
Does this predict a real orbit precisely?
No. The equation gives the ideal two-body Keplerian period and excludes perturbations, drag, and propagation.