mph

Miles per hour (mph) is a unit of speed used primarily in the United States and in a few other countries for measuring how many miles are traveled in one hour. The mile is defined as 5,280 feet or 1,609.344 meters, so mph describes speed relative to the mile as a unit of distance.

Conversions are commonly needed. 1 mph equals 0.44704 meters per second; 1 meter per second equals about 2.23694 mph. In metric terms, 1 mph is about 1.60934 kilometers per hour. For reference, 1 knot (nautical mile per hour) is exactly 1.15078 mph.

Geographic and practical usage varies. mph is widely used for road speed limits and vehicle speeds on signs in the United States and, to varying extents, in some other regions. In many other countries, speed limits are posted in kilometers per hour. Aviation and meteorology often use knots or kilometers per hour respectively, while mph can appear in certain manuals or consumer contexts within those fields.

mph is a non-SI unit. In scientific contexts, speed is commonly expressed in meters per second or kilometers per hour, while everyday travel and consumer discussions in the U.S. frequently employ mph. The unit remains a cultural and regulatory default for speed measurement in road traffic in the United States, even as metric usage increases in other domains and regions.