Circle of fifth

The circle of fifth is very usefull to know how many accidentals there are in a key or a scale.

For example, we want to build a D Major scale.

When we look at the circle of fifth we can see that the letter D is in the second position starting from the letter C.

It means that the D scale has two sharps.

If we want to build an A flat scale, we look at the letter A and see that it is in the fourth position. So it has 4 flats.

The letters in green are the Relative minor chords of the letters in black.