While most stationary bicycles measure speed in terms of miles per hour, not all of these measure cadence in terms of revolutions per minute. By monitoring cadence, or the number of revolutions of the wheel crank per minute, cyclists can maintain a consistent level of exertion throughout their workout. A goal of many elite cyclists is to maintain a cadence of between 85 to 95 rpm, which allows them to efficiently cover the desired distance without wasting energy. Fortunately, conversion of mph to rpm can be accomplished by using a few simple mathematical calculations.
Convert mph to feet per hour. Since there are 5,280 feet in one mile, you will multiply mph by 5,280. For example, a rate of 10 mph is equivalent to 52,800 feet per hour.
Multiply feet per hour by 12 to obtain inches per hour, since there are 12 inches in a foot. For example, 52,800 feet per hour equals 633,600 inches per hour.
Convert inches per hour to inches per minute by dividing inches per hour by 60, as there are 60 minutes in an hour. For example, 633,600 inches per hour equals 10,560 inches per minute.
Look up the wheel circumference in inches in the owner's manual. Alternatively you can contact the manufacturer for this information. While you can estimate the circumference of your wheels by multiplying the diameter, or distance across one tire, by the circumference of a circle, or 3.14, this measurement is imprecise.
Divide the inches per minute by the wheel circumference to obtain rpm. For example, if you have an 80-inch wheel circumference and are bicycling at a rate of 10,560 inches per minute, your cadence would be 132 rpm.
Brenda Scottsdale is a licensed psychologist, a six sigma master black belt and a certified aerobics instructor. She has been writing professionally for more than 15 years in scientific journals, including the "Journal of Criminal Justice and Behavior" and various websites.