how to figure out the key of a song

[taylor414]

just been lookin into music theory and all that fun stuff, and was wondering how you figure out which key a song is in the first place. you said trippin' billies is in A major Bm or Dmajor, is it basically just the chord progession of the song broken down? like in billies its A, Bm, C, D. Ive heard form different things, for example the first chord hit is the key of the song. ANy help will be good, like a website etc.
thanks[/i]

[taylor414]

i mean A, D, C, Bm i think

[LizardHands]

Well, best way to do it is to spell out all the chords, then find what key fits. This however gets screwed up when you get jazz tunes or dave tunes that change keys all over the place. But in the example of billies, if its A, D, C, Bm, then you have the following notes: (btw, i dont know if these are the chords, just going from what you give me)

A C# E
D F# A
C E G
B F# D

Only accidentals are C# and F#, therefore its in D major or your relative minor, B minor

First chord thing is essentially bs. Sometimes when notating music down, people just stick it in the key that makes it easier to read, when it may infact be in a completely different key.

Hope this makes sense, been a long day

Peace