Is this the correct method to figuring out which chords are in which key?


Key of G: G, A, B, C, D, E, F#

Chords in key of G: G, Am, Bm, C, D, Em, F#dim?

thanks for all help
That, obviously enough, is G major only though; minor keys start on the 6th of the relative major scale. So the chords from G major also fit into E minor.

Other than that, you're right, the next part is to work out the extensions (7ths) of the chords
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You got it. Just apply that pattern (Major, minor, minor, major, major, minor, diminished) to any major scale to get the standard chords in other major keys aswell.