Key Signatures for Piano: Sharps, Flats and Relative Minor

A key signature shows the sharps or flats that normally apply throughout a piece. It narrows down the likely key, but does not by itself tell you which note sounds like home.

Read sharp signatures

Sharps are added in the order F–C–G–D–A–E–B. For a major key, go one semitone above the last sharp to find the tonic. With F# and C#, the last sharp is C#; one semitone above it is D, so the major key is D major.

Read flat signatures

Flats are added B–E–A–D–G–C–F. With two or more flats, the second-to-last flat names the major key. Bb and Eb give Bb major. Bb, Eb, Ab and Db give Ab major. The exception to memorise is one flat: F major. No sharps or flats gives C major or A minor.

Listen for the relative minor

The relative minor starts on scale degree six of the major scale. D major and B minor share F# and C#. They have different tonics, and a B-minor passage may use A# as the raised leading note. Such an accidental does not automatically change the printed key signature.

Look at the bass, phrase endings and cadence, then confirm by listening. A piece can modulate while retaining the original printed signature, with local accidentals handling the change.

Connect the signature with chords

In D major, the notes are D–E–F#–G–A–B–C#. The diatonic triads are D, Em, F#m, G, A, Bm and C# diminished. Play D–G–A–D and hear the tonic return.

Keep the spelling of altered chords separate from the key signature. For example, A7(b9) is A–C#–E–G–Bb; A7(b13) contains F natural as its altered thirteenth. G is the minor seventh of A, and Bb is its flattened ninth—not its flattened thirteenth.

Use a short checking routine

1. Name the written accidentals in order.
2. Identify the relative major/minor pair.
3. Find the tonic by listening to a phrase ending.
4. Play I–IV–V–I in the major key, or the relevant minor-key cadence.

Work through Major Scales in 12 Keys and compare the keys in the Circle of Fifths.