question: How do you calculate speed in the U.S.? answer: Speed = distance over time paragraph: Speed is an important aspect of motion. It is a measure of how fast or slow something moves. To determine speed you must know two things. First, you must know how far something travels. Second, you need to know how long it takes to travel that far. Speed can be calculated using this formula: speed = distance time A familiar example is the speed of a car. In the U.S., this is usually expressed in miles per hour. Think about a trip you and your family made in the car. Maybe the trip covered 120 miles and it took 3 hours. What was the cars speed? speed = 120 mi = 40 mi/h 3h The speed of a car may also be expressed in kilometers per hour (km/h). The SI unit for speed is meters per second (m/s). This is the unit of measure a scientist would use. 