How to Convert MPH to RPMs on a Stationary Bike
RPM is an abbreviation for “revolutions per minute.” The term defines the number of complete turns a wheel makes in one minute. Many stationary bikes include instruments that report the device’s RPM rate while you’re exercising. Some bikes, however, may only report your speed in miles per hour. To gain a consistent measure of your performance, therefore, you may wish to convert the miles per hour reported by one bike into revolutions per minute.
Convert the miles per hour into feet traveled per hour. There are 5,280 feet in a mile, so multiply the bike’s miles per hour reading by 5,280. For example, if the reading is 10 miles per hour: 10 times 5,280 = 52,800 feet per hour.
Convert feet per hour into inches per hour. In the example above, 52,800 feet per hour times 12 inches equals 633,600 inches per hour.
Convert inches per hour into inches per minute. For example, 633,600 inches per hour divided by 60 minutes yields a result of 10,560 inches per minute.
Calculate the circumference of the bike’s wheel. Use a tape measure or yardstick to determine the wheel’s diameter -- a straight line running from edge to edge, through the wheel’s center -- then multiply the diameter times pi. For example, if the wheel’s diameter is 25 inches, then 25 times 3.1416 = 78.54 inches.
Divide your inches per minute number by the wheel’s circumference. To conclude the example: 10,560 divided by 78.54 = 134.45 rpm.
M.L. Rose has worked as a print and online journalist for more than 20 years. He has contributed to a variety of national and local publications, specializing in sports writing. Rose holds a B.A. in communications.