Orbital Period Calculator

How it works

1. 1Choose a central body (Earth, Sun, Mars, Jupiter, Moon, or Custom) and enter its mass if using Custom mode.
2. 2Enter the orbital radius in kilometres — measured from the centre of the central body to the orbiting object.
3. 3The calculator applies T = 2π·√(r³ ÷ GM) and displays the period in seconds, minutes, hours, and days.

Use cases

• Verify a low-Earth-orbit satellite completes one pass every ~90 minutes.
• Estimate how long a spacecraft takes to orbit Mars at a given altitude.
• Determine the orbital period of a custom body in a binary-star or exoplanet system.

Frequently asked questions

What formula is used?

Kepler’s third law: T = 2π·√(r³ ÷ GM), where r is the orbital radius in metres, M is the central mass in kg, and G = 6.6743×10⁻¹¹ N·m²/kg². The result T is the orbital period in seconds.

Does the period depend on the orbiting object’s mass?

No. T depends only on the orbital radius r and the central body’s mass M. The satellite’s own mass has no effect — a feather and a spacecraft at the same altitude share the same period.

What is a worked example for low Earth orbit?

The ISS orbits ~400 km up, so r ≈ 6,771 km. With Earth’s mass 5.972×10²⁴ kg: T = 2π·√((6,771,000)³ ÷ (6.6743×10⁻¹¹ × 5.972×10²⁴)) ≈ 5,557 s ≈ 92.6 minutes, matching the ~90-minute ISS orbit.