How to Calculate RPM

Step-by-Step Guide

1. 1

   Step 1: Pick a place on the rotating object to observe.

   This method works best for objects with long arms, such as an anemometer (device to measure wind speed) or wind turbine.
   
   Select an arm or blade to focus your observations on.
   
   You can mark the arm or blade in some way, such as by tying a colored thread or applying a dab of paint to the surface.
2. 2

   Step 2: Get a timer.

   You need something to monitor the time with.
   
   A stopwatch or timer app on a smartphone or tablet works well for this. ,, Be sure to count only when the marked arm or blade returns to the position at which it started. , This is how many revolutions per minute, or RPM, the object makes.
   
   Instead of stopping the count at 1 minute, you may want to count for 2 or 3 minutes and then divide the count by the number of minutes to get the RPM if the object rotates slowly.
   
   This will help you avoid estimating a partial rotation if the object does not return to its original position at the end of 1 minute.
   
   If the object rotates quickly, you may instead want to count for only 15 seconds and then multiply the result by 4 to get the RPM.You can relate the RPM of an object turned by wind to the actual wind speed by first finding the circumference traveled by one of the object’s arms in one rotation.
   
   You then convert this distance to either miles or kilometers and multiply that by the RPM to determine how much distance the object rotated through in 1 minute.
   
   Multiply this by 60 to determine how much distance was traveled in 1 hour, and you’ll have the wind speed
3. 3

   Step 3: Start the timer.

4. 4

   Step 4: Start counting the number of rotations your marked arm or blade makes.

5. 5

   Step 5: Stop counting when 1 minute has elapsed.

Detailed Guide

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