The order of flats beginning with B goes down in perfect 5ths.

B.....5th.....E.....5th.....A.....5th.....D.....5th.....G.....5th.....F

An easy way to remember this is the sentence :

Blanket Exploded And Dad Got Cold Feet

To find the key signature of a Major flat keyremember that this will be the last flat but one.

To find the relative minor, simply go down three semitones (minor 3rd).

Example

To find the key signature of A flat major, go 1 flat further in order of flats and the key signature will be Bflat, E flat, A flat and D flat.