- 1). Ask your licensed driver assistant to drive at a constant speed on a road with mile markers--or have an assistant help as you reach a constant speed.
- 2). Start the stopwatch at the exact moment the car passes a mile marker--be sure to watch the road for mile markers.
- 3). Drive at constant speed for three miles.
- 4). Stop the stopwatch as you reach the fourth mile marker (three miles driven) and record the total time--for example, it might take you two minutes and fifteen seconds to travel three miles.
- 1). Convert total time to a decimal--multiply the number of minutes by 60 seconds/minute (e.g., 2 x 60 = 120), add the number of seconds (e.g., 120 + 15 = 135) and divide the total by 60 seconds to find the decimal minutes (e.g., 135/60 = 2.25 minutes).
- 2). Divide the total travel time by three--the number of miles driven--to determine average minutes per mile. In this example, 2.25 minutes/3 miles = average of 0.75 minutes per mile.
- 3). Divide 60 (minutes per hour) by your average minutes per mile to find miles per hour (e.g., 60/0.75 = 80 miles per hour).
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