count 4 8 16 32 64 beats.
seconds
seconds/beat
BPM

This JavaScript app is useful for finding the approximate BPM of a song. Due to the limitations of JavaScript, it is not extremely accurate, but the values should be close enough for most purposes. (The accuracy will also depend greatly on the speed of your computer. A faster computer = more accurate results.)

Instructions:

1. Select how many beats to count. (The more beats you count, the more accurate your results are likely to be.)
2. Click START/STOP on a downbeat
3. Count the selected number of beats.
4. Click START/STOP on the next downbeat after the selected number of beats.

E.g. if you've selected 8 beats, you would count:

*click*                                                         *click*
   1       2       3       4       5       6       7       8       9