What a Key Signature Is

  • A key signature is a group of sharps (#) or flats (♭) written at the start of a staff.
  • It tells you which notes are consistently raised or lowered throughout the piece.
  • This defines the tonal center (the “home” note) and the scale the music is based on.

Circle of Fifths
The easiest way to learn key signatures is through the Circle of Fifths:

  • Sharps: Each new key adds one sharp in this order → F, C, G, D, A, E, B.
  • G major → 1 sharp (F#)
  • D major → 2 sharps (F#, C#)
  • A major → 3 sharps (F#, C#, G#)
  • Flats: Each new key adds one flat in this order → B, E, A, D, G, C, F.
  • F major → 1 flat (Bb)
  • Bb major → 2 flats (Bb, Eb)
  • Eb major → 3 flats (Bb, Eb, Ab)

Quick Tricks to Identify Keys

  • Sharps: Look at the last sharp written → the key is a half-step above it.
  • The key of D has the sharps F# – C# the last sharp being C#
  • So: Last sharp is C# → key is D major.
  • key of ? – F# – C# – G#, one semitpne up from G# = A
  • You try: F# – C# – G# – D# = key of ?
  • Flats: Look at the second-to-last flat → that’s the key.
  • Example: Two flats (Bb, Eb) → key is Bb major.
  • key of ? – Bb – Eb – Ab = Key of Eb
  • You try: Bb – Eb – Ab – Db = key of ?
  • No sharps/flats: That’s C major (or A minor).

Why They Matter

  • Reading music: Saves you from writing accidentals every time.
  • Improvising/soloing: Tells you which scale fits the chords.
  • Composing: Helps set the mood (bright keys like D major vs. darker ones like Eb minor).
  • Transposing: Lets you shift music into a new key by adjusting the signature.

keys with their chords: each key has a “family” of chords that naturally fit together, built from its scale.

Major Keys and Their Chords
Each major key follows the pattern:
I (major), ii (minor), iii (minor), IV (major), V (major), vi (minor), vii° (diminished).

  • C major C, Dm, Em, F, G, Am, B half diminished
  • G major G, Am, Bm, C, D, Em, F# half diminished
  • D major D, Em, F#m, G, A, Bm, C# half diminished
  • A major A, Bm, C#m, D, E, F#m, G# half diminished
  • E major E, F#m, G#m, A, B, C#m, D# half diminished
  • F major F, Gm, Am, Bb, C, Dm, E half diminished

Minor Keys and Their Chords
Each minor key follows the pattern:
i (minor), ii° (diminished), III (major), iv (minor), v (minor), VI (major), VII (major).

  • A minor Am, B hslf diminished, C, Dm, Em, F, G
  • E minor Em, F# half minished, G, Am, Bm, C, D
  • D minor Dm, E half diminished, F, Gm, Am, Bb, C
  • C minor Cm, D half diminished, Eb, Fm, Gm, Ab, Bb

Visual Chart
Here’s a handy chart that lays out the chords in each major key:

Each of the above chords in their keys are numbered in Roman numerals I – II – III – IV – V – VI – VII.

Above is the major keys of C:

  • C I – D II – E III – F IV – G V – A VI – B VII

Each major key has a relative minor key, this start from the VI chord in the major key, so we re-numbrr the VI chord in the major key to a I chord in minor key.

So lets number the relative minor key of A:

  • A I – B II – C III – D IV – E V – F VI – G VII

Try and figure out some minor key chord numbers for yourself using the visual key chord table above, once you understand how to work out one minor key, then do all the minor keys for each of the major keys.