How long is one year on Mars, measured by the planet's orbit around the Sun?

One year on Mars lasts 687 Earth days, the time Mars takes to complete one orbit around the Sun.

Mars takes longer than Earth to orbit the Sun because its average distance from the Sun is about 228 million kilometres, compared with Earth's roughly 150 million kilometres. Its orbital speed is also slower, so a complete Martian year lasts about 1.88 Earth years.

The seasons on Mars follow this long orbit and are caused by the planet's axial tilt, which is close to Earth's. However, Martian seasons are not equal in length because Mars follows a noticeably more elliptical orbit. Southern-hemisphere summer occurs near Mars's closest approach to the Sun and is therefore shorter and warmer than northern-hemisphere summer.

A Martian year should not be confused with a sol, which is one Martian solar day. A sol is only slightly longer than an Earth day, while a year describes the planet's journey around the Sun.