If 10k is 6.2 miles on land, then 20k is 12.4 miles For an ocean race, the conversion is to nautical miles. The source provides a reference to a yahoo question and answer from the year 2007.Source(s): http://answers.yahoo.com/question/index?...f 10k is 6.2 miles on land, then 20k is 12.4 miles For an ocean race, the conversion is to nautical miles. The source provides a reference to a yahoo question and answer from the year 2007. Source(s): http://answers.yahoo.com/question/index?...