For example, the key of G major scale [G – A – B – C – D – E – F♯ – G] has one F♯. The signature of the key of G major has one sharp on the F.
The key signature indicates that all of the F notes are sharp, and all other F notes in other octaves are also sharp.
If a natural symbol is placed to the left of one of the F note in one of the measure, that F note is played as a natural F note for the rest of the measure. After the measure ends, all F notes are to be played as F sharp again.
If a key signature has no sharp or flat, it means that all notes are naturals.
The C major [C – D – E – F – G – A – B – C] and A minor [A – B – C – D – E – F – G – A] keys contain only natural notes, they have no sharp or flat. C major and A minor have the same relative keys and share the same key signature because A minor is the relative minor of C major.
List of All Major / Minor Key Signatures
Sharp Key Signatures:
G major / E minor has one sharp: F♯
D major / B minor has two sharps: F♯ – C♯
A major / F♯ minor has three sharps: F♯ – C♯ – G♯
E major / C♯ minor has four sharps: F♯ – C♯ – G♯ – D♯
B major / G♯ minor has five sharps: F♯ – C♯ – G♯ – D♯ – A♯
F♯ major / D♯ minor has six sharps: F♯ – C♯ – G♯ – D♯ – A♯ – E♯
C♯ major / A♯ minor has seven sharps: F♯ – C♯ – G♯ – D♯ – A♯ – E♯ – B♯
The Sharp Key Signatures Chart:
The sharp key signatures chart displays all sharps key signatures. All sharps appear in the following order in all sharp key signatures:
F – C – G – D – A – E – B
Flat Key signatures:
F major / D minor has one flat: B♭
B♭ major / G minor has two flats: B♭ – E♭
E♭ major / C minor has three flats: B♭ – E♭ – A♭
A♭ major / F minor has four flats: B♭ – E♭ – A♭ – D♭
D♭ major / B♭ minor has five flats: B♭ – E♭ – A♭ – D♭ – G♭
G♭ major / E♭ minor has six flats: B♭ – E♭ – A♭ – D♭ – G♭ – C♭
C♭ major / A♭ minor has seven flats: B♭ – E♭ – A♭ – D♭ – G♭ – C♭ – F♭
The Flat Key Signatures Chart:
The flat key signatures chart displays all flat key signatures. B – E – A – D – G – C – F is the order of flats in all flat key signatures. Notice that it is the backward of order of sharps [F – C – G – D – A – E – B].
How to determine the key from the number of sharps or flats in a key signature?
Major key – a quick way to determine the major key from a sharp key signature is to raise the last position sharp by a half step to get the major key.
If the key signature has flats, the major key is the name of the second-to-last flat. The only exceptions to this rule are F major and C major, because F major key has only one flat and C major has no sharp or flat.
Minor key – Remember that each major key shares a key signature with a minor key. This minor key is called the relative minor of the major key. For example, E minor is the relative minor of G major, they have the same key signature because E minor and G major have the same relative keys.