Kepler Third Law

Estimate orbital period in years from semi-major axis and central mass using Kepler’s third law.

How this calculator works

Enter the values for first value, second value and review the units before calculating.

Formula / method

P = √(a³ ÷ M)

Worked example

An object at 1 AU around a 1-solar-mass star has a 1-year period.

Assumptions and limitations

The orbit is bound, the central mass dominates, and AU/solar-mass units are used.

Eccentricity, additional bodies and relativistic effects are ignored.

Sources and methodology references