Guide · Guitar theory
Key signatures and the order of sharps and flats
A The sharps or flats written at the start of each line of music, telling you which notes the key changes. lists the sharps or flats a key always uses. Sharps are always added in the order F♯ C♯ G♯ D♯ A♯ E♯ B♯ and flats in the order B♭ E♭ A♭ D♭ G♭ C♭ F♭, so the number of sharps or flats tells you the key.
What a key signature is
It is the group of sharps or flats at the start of each line of music, telling you which notes are raised or lowered throughout.
Instead of writing a sharp next to every F in a song in G major, the music puts one sharp on the F line at the start of each staff. G major has one sharp: F♯. Every F in the piece is played as F♯ unless a natural sign says otherwise.
A key never mixes sharps and flats in its signature, and each letter appears only once. A note raised outside the signature keeps its letter: a flat is raised with a natural (B♭ to B♮ in F major), and a natural note with a sharp (C to C♯ in D minor).
The order of flats
Flats appear in the reverse order, B♭, E♭, A♭, D♭, G♭, C♭, F♭, each a fifth below the last.
Read the sharp mnemonic backwards: 'Battle Ends And Down Goes Charles' Father'. The flats spell the word BEAD, then G, C and F.
To name a flat key, take the second-to-last flat. B♭ major has B♭ and E♭, and the second-to-last is B♭. E♭ major has three flats and the second-to-last is E♭. The one key to memorise is F major, with only one flat, B♭.
Every key by its signature
Each signature belongs to one major key and its The major and minor keys that share all seven notes and the same key signature, such as C major and A minor.; the music's home chord tells you which.
No sharps or flats: C major or A minor.
Sharps: 1: G major or E minor; 2: D major or B minor; 3: A major or F♯ minor; 4: E major or C♯ minor; 5: B major or G♯ minor; 6: F♯ major or D♯ minor.
Flats: 1: F major or D minor; 2: B♭ major or G minor; 3: E♭ major or C minor; 4: A♭ major or F minor; 5: D♭ major or B♭ minor; 6: G♭ major or E♭ minor.
Seven-sharp and seven-flat keys exist too (C♯ major and C♭ major), but they are rare; most music uses their twins with five flats or five sharps. The chart of every key shows all of them with their chords.
Why guitarists should care
The signature tells you which notes to avoid, which keys suit open strings, and how far apart two keys are.
Sharp keys suit the guitar's open strings, which are E, A, D, G, B and E. In G major and E minor (one sharp) every open string belongs to the key. E major has four sharps, but its low E, A and B strings still ring under the chords, which is why so many rock and blues riffs live there. Flat keys such as E♭ and B♭ come up with horns and keyboards, and often mean A chord where one finger presses several strings at the same fret, like a movable nut, so the shape works anywhere on the neck. or a A clamp across all six strings at one fret. It raises every open string, so familiar shapes play in a higher key..
Each step round the circle of fifths adds one sharp or removes one flat, so the signature also tells you where a key sits on the circle and which keys are its neighbours.