What a key signature does
The sharps or flats right after the clef are the key signature. Each one changes every note of that letter, in every octave, for the whole piece (until the key signature changes). In G major there’s one sharp, on the F line, and it means every F you meet is played as F♯: the F at the top of the treble staff, the F in its bottom space, and every F in the bass.
A sharp, flat or natural written beside a note (an accidental) overrides the key signature for that note and any repeat of it until the end of the bar. After the barline, the key signature applies again.
The order of sharps and flats
Sharps are always added in the same order: F, C, G, D, A, E, B, often remembered as “Father Charles Goes Down And Ends Battle”. Flats come in the reverse order: B, E, A, D, G, C, F, “Battle Ends And Down Goes Charles’ Father”. So a key with two sharps always has F♯ and C♯, and a key with three flats always has B♭, E♭ and A♭. You never have to read every sign: count them, and you know which they are.
| Key | Signature | Key | Signature |
|---|---|---|---|
| G major | F♯ | F major | B♭ |
| D major | F♯ C♯ | B♭ major | B♭ E♭ |
| A major | F♯ C♯ G♯ | E♭ major | B♭ E♭ A♭ |
| E major | F♯ C♯ G♯ D♯ | A♭ major | B♭ E♭ A♭ D♭ |
Naming the key
With sharps, the last sharp is the seventh note of the major scale, so the key is one letter up: the last sharp in A major’s signature is G♯, and A is the next note up. With flats, the second-to-last flat names the key: B♭, E♭, A♭ is E♭ major. F major, with a single B♭, is the one to memorise. Each signature is shared by a minor key too (G major’s by E minor), but the notes it changes are the same, and that’s what this quiz asks.
Common mistakes
- Forgetting it altogether. The note looks plain, so you play it plain. This is the most common slip in any piece with a key signature, and the quiz names it when it happens.
- Applying it only where it’s drawn. The treble staff’s F♯ sign sits on the top line, but the F in the bottom space is just as sharp, and so are the Fs on the bass staff.
- Sharpening the wrong note. In D major it’s F and C, not F and G. Count the signs and use the order above rather than reading where each one sits.
A tip for speed
Before you play anything, say the changed notes to yourself: “E♭ major: B, E and A are flat.” Then let it shape your hand, so the black keys feel like part of the position rather than exceptions. Rounds here mix keys on purpose; when one key keeps showing up in your misses, practise its scale once or twice, then come back.
Answer with the note buttons (spelt with sharps in sharp keys and flats in flat keys), the piano, a MIDI keyboard, or the computer keys as a piano. To see key signatures in real music, try the sight-reading exercises; the guides explain scales and keys further.