Donaldson R F Mars Sol Converter
A Martian day — a "sol" — is a little longer than an Earth day. Convert between the two, the way NASA's Mars missions do.
Why Mars has its own day unit
A Mars solar day (a "sol") is 24 hours, 39 minutes and 35 seconds long — about 2.7% longer than an Earth day, because Mars spins slightly more slowly. That difference adds up: after 37 Earth days, a Mars rover's "morning" has drifted a full Earth day later. NASA's rover teams work in Mars time using sols rather than Earth days so that mission plans stay lined up with the actual Martian day/night cycle.
One sol equals 1.0274912517 Earth days. Enter a number in either box and the other updates — for example, the Perseverance rover's original prime mission of one Mars year is about 687 Earth days, or about 669 sols.
Frequently asked questions
Is this the same as a Martian year?
No — a Mars year (one orbit of the Sun) is about 687 Earth days, made up of about 668.6 sols. This tool converts individual days, not years; see the Age on Other Planets tool for orbital periods.
Where does the exact conversion factor come from?
It is built into the Mars24 Sunclock algorithm that NASA/GISS publishes for working out the time of day at any point on Mars, cited below.
Related tools: Age on Other Planets, Planet Facts Table, Julian Date Converter.
Source / Last verified: NASA/GISS, "Mars24 Sunclock – Algorithm and Worked Examples" (giss.nasa.gov/tools/mars24/help/algorithm.html), equation C-2, which gives the sol-to-day ratio 1.0274912517. Read and used on 27 September 2026.