First of all, what is a fifth?
A fifth is an interval (a distance between notes). It is simply the distance between the first note of a scale, and the fifth note of that scale. For example, in the key of C a fifth is the distance between C and G. It is very important to remember that it is not just
counting up 5 notes, but five whole notes including any flats or sharps in that scale. For example, in the key of B Major ( which has F#,C#,G#,D#,A# ) if we counted up five notes, we would get to F, whereas in this scale the fifth is infact F#. That is because B major has an F# in it.
What does the circle of fifths do?
The circle of fifths is used to work out what the correct accidentals (sharps or flats) are in any given key, and to show the relationship between the various keys.
How does it work?
At the top of the circle we start with C, with no accidentals, then we simply move up a fifth each time as we progress around the circle in a clockwise direction.
Each time we move one step around the circle, another sharp is added to the scale, so C has no sharps. We then get G which has one sharp, then D which has two, E that has 3, etc.
When we reach 7 steps round the circle we have obviously run out of sharps to add to the list, so now we need to add the flat keys. To do this we follow exactly the same procedure, but going round the circle in an anti-clockwise direction, only this time we go down a fifth each time. So from C we go down to F which has one flat (Bb), if we go down a fifth from F we reach Bb (remembering a fifth is not always simply five notes) and so on.
The sharps or flats ( accidentals ) are always added in the same order. It can be remembered using this rhyme;
reading down the rhyme gives us the order of the sharps and reading it backwards
gives us the order of the flats.
So G major has one sharp F# and D major has two F# and C#, and so it continues…
Using this method you should be able to work out the key sigature for any major key.
The diagram also shows the minor keys which are related to each major key. For more information on how minor keys work,
go to this article.