It stems from sailers and is a measure of speed. It is one nautical mile per hour. Never refer to "knots per hour" unless you want to describe acceleration. A nautical mile is one minute of one degree of longitude and is slightly longer than the ordinary, or statute, mile used in the United States. To convert nautical miles to miles or knots to miles per hour, multiply by 1.15. To convert miles to nautical miles or miles per hour to knots, divide by 1.15.
however some sources say......One knot equals 1.22 miles