Frequently Asked Questions

Kepler's third law states that the square of an orbital period is proportional to the cube of the semi-major axis of the orbit. In its full form, T = 2π√(a³/GM), where G is the gravitational constant and M is the mass of the central body.

The semi-major axis is half the longest diameter of an elliptical orbit. For a circular orbit it equals the radius. It is the key distance measurement used in Kepler's third law.

Yes. Choose a preset central body mass such as the Sun, Earth, Mars, or Jupiter, or enter a custom mass in kilograms for any other star or planet.

Yes. Switch to 'Solve for Semi-Major Axis' mode, enter the known orbital period and central body mass, and the calculator solves Kepler's third law for the distance.

A year is defined as the time Earth takes to complete one orbit of the Sun, roughly 365.25 days, based on Earth's semi-major axis of 1 astronomical unit and the Sun's mass.

The calculator uses the standard gravitational constant and Kepler's third law, giving results accurate to several significant figures for two-body orbital mechanics. It does not account for perturbations from other bodies.

You can enter the semi-major axis in astronomical units (AU), kilometers, or meters. The calculator converts internally to meters for the calculation.

Results are shown in years, days, hours, and seconds simultaneously so you can use whichever unit fits your context.

Yes. Select Earth as the central body and enter the satellite's semi-major axis (its altitude plus Earth's radius) in kilometers or meters.

Yes, the orbital period calculator is completely free with no sign-up, and all calculations run instantly in your browser.