Hi Yopie,

Behringer has a device on which you can tap a button to the beat of the song or .wav file.  And many Pro-tools plug-ins have a "tap tempo" function which then calculates bpm for you.  In the simplest sense, 60 bpm is 1 beat per second.  So, if you are tapping your finger 50 times a minute to your .wav file, the bpm = 50.  This assumes you are using quarter notes when tapping however.  If you tap your finger to your wav file and you noticed you tapped 100 times in a minute, this could mean that you were tapping eighth notes and really, it was 50 bpm and not 100 bpm, since bpm, in the classic sense, is always based on quarter notes. If you are are dealing in different time signatures (e.g. 7/4, 5/4, 3/4, 11/4) you always find what the quarter note pulse is and find out how many times you tap your finger in a minute - and that is your bpm.  Be aware of what a quarter note is - and this should solve it for you. Or, buy a metronome and see what the metronome setting is when it seems to be 'in sync' with your .wav file. What is your .wav file?  A song, sound of ocean waves, something other than music? Heartbeat?  Also, you could have something weird like 90.5 bpm.  As well, if you listen to songs that were not recorded with a metronome, the bpm changes from time to time throughout the whole song. Early Beatles = no metronome (flowing excitement; the beat make sense as the song grows, e.g., "It Won't Be Long"). Sting = perfect metronome (e.g. "Fields of Gold"). Stravinski, Beethoven, Brahms, Mozart... suggested tempos, and rit. (slow downs) and accel. (speed ups)... gas pedal moving up and down. Are you dealing with a perfect bpm?  Only you have the .wav file you are talking about ;]  120 bpm is another very common tempo.  The odd tempos 117, 105, 99 ... have a certain magic to them as well. 

Attached is a tool I made for exploring this sort of thing...

This can be simply find using DAW s (digital audio workstation)using time warp too..........

A tapping finger and a cheap watch will cost you less though ;]

Agree with Jack. Just tap feet or finger to get BPM. 

Article Survey paper on music beat tracking

Manual way: open the file in a sound editor, select a section and play with looping on. Adjust loop length at one end until it sounds in time. Read off the loop length as t seconds. Then bpm = 60/t 

You can also use the MIRToolbox library in Matlab environment to get bpm and beat histogram.