The equivalent of 45 kilometers per hour is 27.96 miles per hour. There are 0.6214 miles in 1 kilometer, so to convert 45 kilometers to miles multiply (45 kilometers)(0.6214 miles/1 kilometer). This gives 27.96 miles.
Since both kilometers per hour and miles per hour use hours for the time unit, there is no need to do any further conversions. The kilometer is the SI unit for length in the metric system, and the mile is a unit of length in the imperial system. The Roman mile equalled 1,000 double paces of their marching soldiers. The British modified the Roman mile to equal 8 furlongs, which is 5,280 feet.