Because 1 kilometer per hour is equivalent to .0.62137119 miles per hour, multiplying 280 kilometers per hour by .6214 creates a value expressed in miles per hour. For this specific answer, 280 kilometers per hour expressed in miles per hour would be 173.98393383 or 174 mph.
Miles per hour is a unit of measuring speed to express the number of miles traveled by a moving object in one hour. It is an imperial and United States customary unit that is still a standard in some countries, as opposed to the more common kilometers per hour used worldwide.
The mph is a standard for roadway usage in countries including the United Kingdom, U.S., the Bahamas, Belize, British Virgin Islands, Dominica, the Falkland Islands, Grenada, Guam, Burma, the Northern Marian Islands, Samoa, St. Lucia, St. Vincent and The Grenadines, St. Helena, St. Kitts and Nevis, Turks and Caicos Islands, the U.S. Virgin Islands, Antigua and Barbuda, and Puerto Rico.
Apart from roadway usage, miles per hour is also used in sporting events such as the speed of the delivery of a pitch in baseball, the speed of a tennis ball after a serve in tennis, or the speed of shuttlecocks after a smash in badminton.