How do you measure BPM...

[kodacolor]

without using a metronome?

If I were listening to a song how could I tell the bpm just by listening to the song?

[BigFoot_BigThumb]

If you have a stopwatch or a clock nearby.  Count for a minute and the number that you get at 60 seconds is your BPM.  Or you can count for 30 seconds and just double it.

[SabianKnight]

without using a metronome?

If I were listening to a song how could I tell the bpm just by listening to the song?

You have to condition your own internal clock to certain BPMs to a metronome first. Once you can accurately feel various quarter note BPMs like 45, 70, 85, 90, 92, 100, 110, 120, 130, 140 you will be able to pretty much determine most song BPMs within 4-5 BPMs. You just listen for the 2 and 4 snare hits most commonly and then fill in the 1 and 3 when counting it in your head or tapping it out. Best way though for you the musician is get you one of these (I know you asked about doing it without a metronome but... ):

Dr. Beat DB-30 http://www.amazon.com/s/ref=nb_ss_b?url=search-alias%3Dstripbooks&field-keywords=Dr.Beat+DB-30&x=0&y=0