The circle of fifths and key signatures

The key is the "home" of a song: the note where everything comes to rest and the scale it uses. The key signature, at the start of the staff, tells you the key without hearing a thing.

The key signature

These are the sharps or flats written next to the clef. They apply to the whole piece: if there is an F♯ in the key signature, every F is played sharp, in any octave.

C major (and A minor) have no sharps or flats at all.

Key signatures with sharps

Sharps always appear in the same order: F, C, G, D, A, E, B. It is not a random order: each one is a fifth above the one before, just like on the circle of fifths.

To find the major key, look at the last sharp and go up a half step: last F♯ → G major; last C♯ → D major; last G♯ → A major.

Why it works: the last sharp added is always the seventh note of the scale, the one a half step below the tonic. In G major (G A B C D E F♯), F♯ is the seventh.

Key signatures with flats

Flats go in the opposite order: B, E, A, D, G, C, F. Each one is a fifth below the one before.

The major key is the second-to-last flat: B♭, E♭ → B♭ major; B♭, E♭, A♭ → E♭ major. The only one to memorize is the single flat (B♭): F major.

Why it works: the last flat is always the fourth note of the scale, and the tonic is a fourth below, which happens to be the previous flat. In B♭ major (B♭ C D E♭ F G A), E♭ is the fourth.

The circle of fifths

It arranges every key like a clock. At the top is C, with no sharps or flats. Going right, each step goes up a fifth (C → G → D…) and adds a sharp. Going left, each step goes down a fifth (C → F → B♭…) and adds a flat.

Why each step adds just one accidental: the new scale uses the same notes as the previous one except one. From C to G only F changes, becoming F♯ so it sits a half step below G. From C to F only B changes, becoming B♭.

That is why neighbors on the circle share almost all their notes and sound good together.

Relative minors

Each key signature works for two keys: a major key and its relative minor. They use exactly the same notes; the only thing that changes is the note where the music comes to rest (the tonic).

So an F♯ in the key signature doesn't just mean "G major": it means "G major or E minor". Both have a single sharp, F♯.

Why they share a key signature

Because they are the same 7 notes: only the starting note changes.

Take the notes of G major and start from the sixth (E), and you get exactly the E minor scale. Since the notes are the same, both carry the same F♯ in the key signature.

What changes when you start on another note is the order of whole steps (W) and half steps (H). That order is what makes major sound bright and minor sadder.

How to find the relative minor

1. Work out the major key with the key signature trick. With one F♯: last sharp + a half step = G major.
2. From there go down 3 semitones, counting every key, black ones included: G → F♯ → F → E. The relative is E minor.

Another way: it is the sixth note of the major scale. G, A, B, C, D, E: E minor. The sixth note is always 3 semitones below the major tonic; that is why both rules work.

The other way round, from the minor go up 3 semitones: E → F → F♯ → G, G major.

On the circle of fifths there is no need to count: the relative sits in the inner ring, right under the major.

Major or minor?

The key signature alone doesn't tell you: you have to look at the music. The easiest clue is the last note (and the last chord): it is almost always the tonic. With an F♯ in the key signature, if the melody ends on G it is G major; if it ends on E, it is E minor.

Another minor clue: an extra accidental that is not in the key signature keeps showing up a half step below the tonic. It is called the leading tone: in E minor it is D♯, which pushes back to E.

Table of keys and key signatures

By Joaquin Varela · Updated November 1, 2026