Harmony
Key signature
A key signature is the group of sharps or flats written at the start of every staff: it tells you which notes are altered throughout the piece, and so points to its key.
What is a key signature?
A key signature is the set of sharps or flats written right after the clef at the start of every line. It applies in every octave, for the whole piece, unless a natural sign cancels it for one note.
One sharp on the F line? Every F becomes F#, low or high. That is the key signature of G major. In short, it summarises the scale of the key so the composer does not have to write an accidental before every note.
What order do sharps and flats go in?
The order never changes, and it follows fifths:
- sharps: F C G D A E B (Father Charles Goes Down And Ends Battle);
- flats: B E A D G C F, the same list reversed (Battle Ends And Down Goes Charles' Father).
So a signature with three sharps always holds F#, C# and G#, never any other combination. This order is exactly the circle of fifths: each key a fifth higher adds one sharp, each key a fifth lower adds one flat.
How do you name the key from a key signature?
Two rules cover everything:
- Sharps: take the last sharp and go up a half step. F# C# G#: last sharp G#, a half step up is A. That is A major.
- Flats: the second-to-last flat is the key. Bb Eb Ab: second-to-last is Eb, so Eb major. The one to memorise: a single flat (Bb) = F major.
Every signature also belongs to a relative minor, a minor third lower: three sharps means A major or F# minor. The music decides (the resting chord, a leading tone of G# or E#).
Key signature chart
| Signature | Major | Minor | Altered notes |
|---|---|---|---|
| none | C | Am | none |
| 1 sharp | G | Em | F# |
| 2 sharps | D | Bm | F# C# |
| 3 sharps | A | F#m | F# C# G# |
| 4 sharps | E | C#m | F# C# G# D# |
| 5 sharps | B | G#m | + A# |
| 6 sharps | F# | D#m | + E# |
| 7 sharps | C# | A#m | + B# |
| 1 flat | F | Dm | Bb |
| 2 flats | Bb | Gm | Bb Eb |
| 3 flats | Eb | Cm | Bb Eb Ab |
| 4 flats | Ab | Fm | Bb Eb Ab Db |
| 5 flats | Db | Bbm | + Gb |
| 6 flats | Gb | Ebm | + Cb |
| 7 flats | Cb | Abm | + Fb |
F# major and Gb major sound identical: they are enharmonic equivalents, like B and Cb, or C# and Db.
Why key signatures matter on guitar too
Tabs and chord charts show no key signature, but it still lives in your fingers. In A major (3 sharps) the G of the scale is G#: on the high E string, 4th fret, not 3rd. In E major add D#: 4th fret of the B string.
Guitarists favour sharp keys (E, A, D, G) because their roots are open strings. To look up any signature in a second, spin the interactive circle of fifths: it shows each key's sharps or flats and its relative minor.
Key takeaways
- Order of sharps: F C G D A E B. Order of flats: B E A D G C F.
- Sharps: last sharp + a half step. Flats: second-to-last flat.
- A major = 3 sharps (F# C# G#); Eb major = 3 flats (Bb Eb Ab).
- One signature = one major key and its relative minor.
Frequently asked questions
How many sharps are in E major?
Four: F#, C#, G# and D#. Its relative minor, C# minor, shares the same key signature.
What is the key signature of D minor?
One flat, Bb, like its relative F major. The C# you often see in D minor comes from harmonic minor and is written as an accidental, not in the key signature.
Can one key signature mean two different keys?
Yes, always two: a major key and its relative minor. Two sharps means D major or B minor. Check the final chord and look for a leading tone (A# in B minor) to decide.
Related terms
Practise in the workshop
Take it from theory to the fretboard
Open the workshop tools and see this idea across the whole neck. Free account, no card needed.