Planets - Calculate Orbit (Year) Length

Calculator for the duration of the planetary orbits around the Sun, in hours, days and years and compared to each other. Planets orbit a star, in our solar system, this star is the Sun. The orbit shapes are ellipses. The time for one orbit is called year. The further away a planet is from its star, the longer the orbit takes and the longer is the year of that planet.

Hours (h):
Days (d):
Years (y):
Length		Hours (Earth-) days (Earth-) years
Mercury:
Venus:
Earth:
Mars:
Jupiter:
Saturn:
Uranus:
Neptune:
Pluto:

Round to   0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15   decimal places.

Please enter one value, the other values will be calculated.

Days (d) refers to the 24 hours of a day on Earth. A year (y) is calculated here as exactly 365.2425 days. The Earth's sidereal year, the time it takes to complete one orbit, is 365.256363 days.

Example: the Mars year is almost as long as 1.9 Earth years, Pluto needs 248 years for one orbit around the Sun.

The duration of an orbit depends on the semi-major axis of the orbital path as well as the masses of the central body and the orbiting body, such as a star and a planet, or a planet and a moon. In our solar system, the star is the Sun, and these orbits here are in relation to it. The semi-major axis of an ellipse, in this case, the elliptical orbit, is the distance from the ellipse's center to one of its two most distant points. The corresponding point on the ellipse is the center of the planet. The center of the ellipse itself, however, lies in space. Notably, it is not the center of the star, as the star is located at one of the ellipse's two foci. The system revolves around the common barycenter.
The greater the masses of the celestial bodies involved, the higher the orbital velocity becomes, thereby reducing the time required for an orbit. Often, the mass of the star is the decisive factor while the planet's mass is negligible, at least within our solar system, though there exist also systems featuring similarly sized partners that orbit one another.
For the exact calculation of the orbit period, see Kepler's 3rd law.

Last updated on 08/06/2026. Author: Jürgen Kummer

Calculators for Planets and Astronomy

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