Nautical measure is a term used to describe the various units of measurement used in navigation and sailing. A LEAGUE is a unit of length equal to three nautical miles, or about 5.6 kilometers. A KNOT is a unit of speed equal to one nautical mile per hour, or about 1.15 miles per hour. A FATHOM is a unit of length equal to six feet, or about 1.8 meters. Knots is a plural form of the KNOT, referring to a speed of multiple knots. Seamile is a unit of length equal to one nautical mile, or about 1.85 kilometers.