Song key determination

Question

How do you determine the key to a song if you know its key signature (the number of sharps and flats)?

Answer 1

If not musically literate -meaning circle of fifths, I suggest a more pragmatic approach. Download Moises or sign up for Fadr. If it's your song, you can upload and split into stems it will determine the key for you and then you probably can spend a little time understanding what the key means -whether by ear OR understanding notation and music theory.

Answer 2

Hi there! See below.

IF THE KEY SIGNATURE HAS SHARPS:

1. Count the number of sharps.
2. Go up a half step (one semitone) from the last sharp listed in the key signature—that gives you the major key.

Example:

1. Key signature has 3 sharps: F♯, C♯, and G♯.
2. Last sharp is G♯.
3. Go up a half step → A major.

To find the relative minor, go down a minor third (3 semitones) from the major key:

1. A major → F♯ minor.

IF THE KEY SIGNATURE HAS FLATS:

1. Count the number of flats.
2. The second-to-last flat is the major key.

Example:

1. Key signature has 4 flats: B♭, E♭, A♭, and D♭.
2. Second-to-last flat is A♭ → A♭ major.

(If there’s only 1 flat, it’s always F major.)

The relative minor is a minor third below the major:

1. A♭ major → F minor.

Summary Table:

Sharps/FlatsMajor KeyMinor Key
0	C major	A minor
1 sharp	G major	E minor
2 sharps	D major	B minor
3 sharps	A major	F♯ minor
4 sharps	E major	C♯ minor
5 sharps	B major	G♯ minor
6 sharps	F♯ major	D♯ minor
7 sharps	C♯ major	A♯ minor
1 flat	F major	D minor
2 flats	B♭ major	G minor
3 flats	E♭ major	C minor
4 flats	A♭ major	F minor
5 flats	D♭ major	B♭ minor
6 flats	G♭ major	E♭ minor
7 flats	C♭ major	A♭ minor