The length of time for Mars to complete one orbit around the Sun is its sidereal year, and is about 686.98 Earth solar days, or 668.5991 sols. Because of the eccentricity of Mars' orbit, the seasons are not of equal length.
https://en.wikipedia.org/wiki/Timekeeping_on_Mars
A proposed counterpart on Mars is the Mars Sol Date (MSD), which is a running count of sols since December 29, 1873 (coincidentally the birth date of astronomer Carl Otto Lampland). Another proposal suggests a start date (or epoch) in the year 1608 (invention of the telescope).
https://en.wikipedia.org/wiki/Timekeeping_on_Mars
1 Solar Longitude is given in degrees and thus ranges from 0 to 360.  Martian Years are numbered according to the calendar proposed by R. Todd Clancy (Clancy et al., Journal of Geophys. Res 105, p 9553, 2000): Martian Year 1 begins (at a time such that Ls=0) on April 11th, 1955.
http://www-mars.lmd.jussieu.fr/mars/time/martian_time.html
The term sol is used by planetary astronomers to refer to the duration of a solar day on Mars. A mean Martian solar day, or sol, is 24 hours, 39 minutes, and 35.244 seconds. When a spacecraft lander begins operations on Mars, the passing Martian days (sols) are tracked using a simple numerical count.
https://en.wikipedia.org/wiki/Timekeeping_on_Mars
Simply enter the desired Earth date and time , or click on the buttons to ( re - ) set these values , and then click on the  Convert Earth Date and time to Martian Date and Solar Longitude  button to obtain the corresponding Mars date ( note that the Julian date corresponding to the supplied Earth date is also given on output but may not be ...
http://www-mars.lmd.jussieu.fr/mars/time/martian_time.html
Confidence votes 11.9K. I will compare the Martian Sol (the Mars solar day) with the solar day on Earth. The Sol is about 39 minutes and 35 seconds longer than Earth's solar day of 24 hours. Thus, the answer is: about 0.9732 days on Mars equals 1 Earth day. I will compare the Martian Sol (the Mars solar day) with the solar day on Earth. The Sol is about 39 minutes and 35 seconds longer than Earth's solar day of 24 hours.<br />Thus, the answer is: about 0.9732 days on Mars equals 1 Earth day.
http://www.answers.com/Q/How_many_days_on_mars_equal_1_earth_day
The average length of a Martian sidereal day is 24h 37m 22.663s (88,642.66300 seconds based on SI units), and the length of its solar day (often called a sol) is 24h 39m 35.24409s (88,775.24409 seconds). The corresponding values for Earth are 23h 56m 4.0916s and 24h 00m 00.002s, respectively.
https://en.wikipedia.org/wiki/Timekeeping_on_Mars
1 Javascript is used for the computations; so if your browser doesn't use Javascript, either because it can't (a rare event) or because its enable Javascript option is turned off (most likely), the interface won't work.  Solar Longitude is given in degrees and thus ranges from 0 to 360.
http://www-mars.lmd.jussieu.fr/mars/time/martian_time.html
The problem is that there are two main definitions of a planet's day. 1) The rotation period, relative to the distant stars is the sidereal day. For Venus that's 243 Earth days. 2) The solar day, based on the position of the Sun in the sky.
https://www.quora.com/How-many-Earth-days-are-equivalent-to-one-day-on-Venus
Given values of Sol number are also strictly (albeit rounded to be given as integers and such that a martian year begins at sol number 1) computed from Ls values. Note that because a martian year spans 668.6 sols, the last (669th) sol of the year is thus, with this simplistic labeling, much shorter than the others.
http://www-mars.lmd.jussieu.fr/mars/time/martian_time.html
how many days in a mars sol
There are 686.98 Earth solar days in a Mars SOL. There are 686.98 Earth solar days in a Mars solar day.