Kepler's Third Law Calculator

Find an orbital period from the semi-major axis (around the Sun).

Orbital period (years) 1

Formula: T² = a³ (in years and AU)

Step-by-step with your numbers:

1. Values used:

2. Semi-major axis = 1 AU

4. Orbital period = Semi-major axis squared = 1 x 1 = 1years

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Kepler's third law links a planet's orbital size to its period.

The math behind it

For Sun-orbiting bodies, T² = a³ when T is in years and a in astronomical units.

Mars at 1.524 AU → about 1.88 years.

Does it work for other stars?

Yes, with the full form T² = 4π²a³/(GM) using the central mass.