How Is Speed Measured?

Martin Barraud/Caiaimage/Getty Images

Measuring speed requires time (T) and a known distance (D). Using the formula distance = rate x time (D=R*T), one determines the average speed by dividing distance by time, or R = D/T. This method assumes the object being measured is already in motion.

  1. Determine the units

    Time units are always in hours, minutes or seconds. Distance units can be either metric or imperial.

  2. Select a known distance based on the units chosen

    Select two points, A and B, to represent the known distance. It should be long enough to make an accurate time measurement. The shorter the distance, the more precise the time measurement must be.

  3. Observe the object at point A, and begin timing

    As the object passes point A, start measuring the time. Using second hands on a watch or stopwatch increases accuracy when using shorter distances.

  4. Observe the object at point B, and stop timing

    Note the elapsed time the object took to travel between the two points.

  5. Divide the distance by the time to obtain an average speed

    Using the formula R = D/T, determine the average rate of speed. This is usually expressed as distance per time unit.