a little experiment
If you are trying to find BPM of a wav using
MixMeister or (any other Bpm calc?),
You need to have a file of at least 16 bars.
I took a 120 BPM click track generaed by Audacity,
and made seperate files of varying bar lengths, and
input them into MixMeister (see below).
You will not get an accurate Bpm with anything less
than 16 bars, - so if you have a smaller file, then
you need to copy/paste til you have at least 16 bars.
BPM test
Drats… I just can’t stand it…
I have this other DAW that has some AMAZING tools for beat mapping an existing music file… but I ain’t gonna name names… 
D
I’m almost sure I’ve posted this little utility before, but maybe not - Tap Tempo
Run it, tap the spacebar in time to the music, read the BPM.