Relative keys have the same key signature (number of sharps or flats). For every note in the chromatic scale there is a relative major scale and a relative minor scale. It is a really good tool when you are composing as it makes it very easy to modulate (change key) from the relative major to the relative minor or vice versa. This will make your compositions instantly more interesting.
How to work out the Relative minor
It’s easy! If you want to get from the relative major to the relative minor you need to count down 3 semitones from the relative major. Have a look at this example:
If I want to get from C major to its relative minor I start on C and count down 3 semitones and reach A. Therefore, the relative minor is A minor.
Here’s another example:
If I want to get from E to its relative minor, again I count down 3 semitones and reach C sharp. So, the relative minor of E major is C sharp minor.
How to work out the Relative major
Again, it’s very easy! All you need to do is to count up 3 semitones from the relative minor and you will reach the relative major. Have a look at this example:
I want to get from F sharp minor to its relative major. Count up 3 semitones and I get to A major. So, the relative major of F sharp minor is A major.