Obtain a stopwatch, time piece with a second hand or digital watch that indicates seconds.
Listen to the song enough to determine the beat, or pulse, of the song or section of a song.
Count the beats of the song while using the time device, preferably a stopwatch, to measure 15 seconds.
Multiply that number by four to get an estimate of the song's tempo in beats per minute.
Obtain a free BPM counter from the Internet. This type of software will analyze a song and accurately determine the tempo in beats per minute.
Download and install freeware such as the industry standard Mixmeister DJ Mixing Software.
Load the selection into the program and allow it to analyze and report the tempo.
Obtain a free program from the Internet that uses the tap method to determine BPM.
Download and install freeware such as Fruity Loops or Ableton Live and become familiar with the interface.
Play the song and start the program while clicking on each beat of the music with the computer mouse.
Wait as the program reports the tempo in beats per minute.