Key Signature Calculator

Key signatures identify the tonal center of a piece of music and tell musicians which notes are consistently sharpened or flattened throughout. The pattern of sharps and flats follows a precise mathematical circle called the Circle of Fifths.

Circle of Fifths formula: Each move clockwise adds one sharp (raises the 7th scale degree). Each move counterclockwise adds one flat (lowers the 4th scale degree).

Order of sharps (by accumulation): F C G D A E B Order of flats (by accumulation): B E A D G C F

Memory aid for sharps: “Father Charles Goes Down And Ends Battle” Memory aid for flats: “Battle Ends And Down Goes Charles’s Father” (reverse of sharps)

Major key identification:

• Sharp keys: The key is one half-step above the last sharp. Four sharps, taken in order, are F♯ C♯ G♯ D♯, so the last is D♯ and the key is a half-step above that: E major.
• Flat keys: The key is the second-to-last flat. Four flats in order are B♭ E♭ A♭ D♭, so the second-to-last is A♭ and the key is A♭ major.

Both rules read straight off the accumulation orders above. Take them in order and never skip: the fourth sharp is always D♯ because F, C, G, D is where the sequence has got to by then.

Relative minor: Every major key shares a key signature with its relative minor, located a minor third (3 semitones) below the major tonic.

• C major → A minor (no sharps or flats)
• G major → E minor (1 sharp: F#)
• F major → D minor (1 flat: Bb)

Scale degree names:

• 1st: Tonic | 2nd: Supertonic | 3rd: Mediant | 4th: Subdominant
• 5th: Dominant | 6th: Submediant | 7th: Leading tone

Number of accidentals by key:

• C major / A minor: 0
• G major / E minor: 1 sharp
• D major / B minor: 2 sharps
• A major / F# minor: 3 sharps
• E major / C# minor: 4 sharps
• F major / D minor: 1 flat
• Bb major / G minor: 2 flats
• Eb major / C minor: 3 flats
• Ab major / F minor: 4 flats

Worked example: A piece has 3 flats. Flats accumulated in order: Bb, Eb, Ab.

• Second-to-last flat = Eb
• Key = Eb major
• Relative minor = Eb − 3 semitones = C minor
• Scale = Eb, F, G, Ab, Bb, C, D, Eb

Every G in the piece is natural, every A and B and E are flatted.