About the Orbital Period Calculator
A Kepler's third law calculator for orbital mechanics, in your browser.
What it is
The Orbital Period Calculator solves Kepler's third law, T = 2ฯโ(aยณ/GM), to find how long it takes an object to orbit a central body. Enter a semi-major axis and central mass to get the period, or enter a known period to solve for the semi-major axis instead. It's built for students, astronomy enthusiasts, and anyone estimating satellite or planetary orbital mechanics.
Features
Two solve modes
Solve for orbital period or for semi-major axis, whichever value you're missing.
Preset central bodies
Choose the Sun, Earth, Mars, Jupiter, or enter any custom mass.
Multiple units
Enter distances in AU, km, or m; periods in years, days, or hours.
Step-by-step working
See the full substitution into Kepler's third law, not just the final answer.