How to Calculate a Speedometer for an Exercise Bike

Stationary bikes often display revolutions per minute (RPMs) rather than your speed. While RPMs can be a good gauge of your effort, you might prefer to calculate your equivalent speed. To do this, you simply need to convert RPMs to miles per hour (mph).

Things You'll Need

  • Tape measure
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Instructions

    • 1

      Measure the diameter of the stationary bike wheel, from one side to the other across the hub, using the tape measure.

    • 2

      Multiply the diameter of the wheel by Pi -- that is 3.14 -- to get the circumference. For instance, if the wheel has a 26-inch diameter it would have a 81.64-inch circumference.

    • 3

      Multiply the circumference by the RPM displayed on the stationary bike to get the equivalent distance traveled in one minute. For instance, at an RPM of 90 the rotation would be equal to traveling 7,347 inches with a 81.64-inch wheel circumference.

    • 4

      Multiply the distance by 60 to get the distance traveled in one hour. For example, if you travel 7,347 inches in one minute, that would be equal to 440,820 inches per hour.

    • 5

      Convert the inches per hour to mph by dividing by 63,360 -- the number of inches in a mile. For instance, 440,820 inches per hour is equal to 7 mph.