The International Space Station circles Earth every 92 minutes because Johannes Kepler said it must, four centuries before it existed. Kepler's third law ties an orbit's period to its size: the period squared equals a constant factor times the orbital radius cubed, written T² = (4π²/GM) × r³, where M is the planet's mass. Double the radius and the period grows by nearly three times — the reason geostationary satellites sit exactly 22,236 miles up, circling once per day in lockstep with Earth's spin.

This calculator handles the multiplication at the core of Kepler's law. Type the orbital factor 4π²/(GM) — for Earth it is about 9.91 × 10^-14 s²/m³ — into Variable A, and the orbital radius cubed into Variable B; the Result box gives the period squared, and one square root later you have the orbital period. A ham-radio operator in Texas planning a contact through a cubesat can check its pass timing, and a student can verify why the Moon takes 27.3 days to circle us. Use meters for the radius and seconds fall out; use miles and the period still works if the factor matches.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Orbital Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.