Select a piece of music that is at least 90 seconds long and maintains a stead tempo. Play the music, and listen to identify the regular beat or rhythm of the music. Tap this beat with your hand or foot.
Start the music playing again from the beginning. Start your stopwatch, and count how many times you tap the beat of the music in 60 seconds. Write down the number of the beats you tapped.
Repeat Step 2 twice more. This will give you three different measurements of the number of beats tapped in a minute while listening to the music. These numbers should be in a similar range, although there might be a slight difference between the three measurements.
Add your three measurement numbers together to yield the total number of beats measured in 3 minutes.
Divide this three-minute total number by three. This number is the average beat frequency, in beats per minute, of the music.