I’ve recorded some Hydrogen drums along with Audacity’s own click function. Now I wonder… is there an easy way to check the tempo of the song? I mean, I might want to change the tempo later on and then it might be practical knowing the tempo. I haven’t saved any of the Hydrogen files, I only exported them as wav:s.
A very accurate way to determine the tempo of a click track, or a drum track, is to select an exact number of beats.
Here I have selected exactly 9 full bars of a 4/4 click track, so that is 36 beats.
As you can see in the Section Toolbar at the bottom, the length is 16.364 seconds.
To work out the bpm temp, divide the number of beats by the duration (36 / 16.364), which gives the number of beats in 1 second, then multiply by 60 to give the number of beats in one minute (bpm):
(36/16.364) x 60 = 131.997 bpm.
The actual tempo of the click track was 132 bpm, but our answer was accurate to within 0.003 bpm.
Further to Steve’s reply, if you recorded to a click track in this Audacity session you can open Click Track to see the BPM you last specified. 
You don’t even need to get your calculator out. Just tap to the beat using:
http://www.all8.com/tools/bpm.htm
which will detect the BPM reasonably accurately in a few taps.
There are some experimental Nyquist plug-ins on this Forum such as Tempo estimation to detect beats then calculate the BPM but really you can work out the beat more accurately by ear or calculator in most cases.
Gale
That’s what I hoped for, but how do I open the click-track?
The same way you created the Click Track in the first place. Generate > Click Track… and look in the Tempo [beats per minute] box for the value you last entered.
Gale
Did that now but it doesn’t work. It only suggests 120 bpm.
As previously explained, that only works in the same Audacity session. If you quit Audacity, the BPM setting will revert to the default 120 BPM.
It is not hard to use a calculator or tap to the beat in your browser.
Gale
Yes, that’s how I’ll do if it becomes necessary.