Key signatures: reading them at a glance
Music theory · Scales and keys · Level 3 · 12 min
Writing a ♯ before every F in a piece in G major would be tedious. So the scale's accidentals are written once and for all at the start of every staff, right after the clef: the key signature. It applies to every octave and throughout the piece (unless the signature changes).
The order of sharps and flats
Accidentals always appear in the same order:
- Sharps: F – C – G – D – A – E – B (each new sharp is a fifth above the previous one) — "Father Charles Goes Down And Ends Battle";
- Flats: B – E – A – D – G – C – F (exactly the reverse) — "Battle Ends And Down Goes Charles's Father".
M:4/4 L:1/4 K:G G4 | [K:D] D4 | [K:A] A4 | [K:E] E4 | [K:B] B4 | [K:F#] F4 | [K:C#] C4 |] w: G D A E B F♯ C♯
M:4/4 L:1/4 K:F F4 | [K:Bb] B4 | [K:Eb] E4 | [K:Ab] A4 | [K:Db] D4 | [K:Gb] G4 | [K:Cb] C4 |] w: F B♭ E♭ A♭ D♭ G♭ C♭
Finding the key in two seconds
- Sharps: the last sharp is the leading tone. Go up a half step: that's the major tonic. Three sharps (F, C, G) → G♯ + half step = A major.
- Flats: the second-to-last flat is the major tonic. Four flats (B, E, A, D) → A♭ major. One exception to memorise: one flat = F major.
- No accidentals: C major (or A minor).
| Signature | Major | Relative minor |
|---|---|---|
| — | C | A |
| 1♯ | G | E |
| 2♯ | D | B |
| 3♯ | A | F♯ |
| 4♯ | E | C♯ |
| 5♯ | B | G♯ |
| 6♯ | F♯ | D♯ |
| 7♯ | C♯ | A♯ |
| 1♭ | F | D |
| 2♭ | B♭ | G |
| 3♭ | E♭ | C |
| 4♭ | A♭ | F |
| 5♭ | D♭ | B♭ |
| 6♭ | G♭ | E♭ |
| 7♭ | C♭ | A♭ |
Major or minor? One signature serves two keys (see "Relative keys"). To decide, look at the last bass note, and look for the minor key's leading tone: with an empty signature, frequent G♯ accidentals point to A minor.
The sight-reader's reflex: before playing a single note, identify the signature, name the key, and play its scale once. Your fingers will "know" where the black keys are. Half of all sight-reading wrong notes come from a forgotten key signature.
Common mistake: applying a signature sharp only to the line or space where it is drawn. The F♯ of G major's signature applies to every F, in every octave.