Key signatures

Up to seven sharps can sit at the start of a staff, and they always appear in the same order: F, C, G, D, A, E, B.

Why write the accidentals once

A piece in E major uses F♯, G♯, C♯ and D♯ in nearly every bar. Writing a sharp beside each of those notes would clutter the page, so composers gather them into a key signature at the start of every line. The signature goes right after the clef and before the time signature, which is easy to remember because the order is alphabetical: clef, key, time. A sharp on the top line of the treble staff means every F is played as F♯, in every octave, until the signature changes.

A key signature lists the accidentals of the major scale on that key's tonic, and nothing else. It never mixes sharps and flats, because no major scale needs both. It works in both directions: read the signature and you can name the key, or start from the key and you can write its signature. The rest of this unit gives you shortcuts for both.

The order of sharps and flats

Sharps always appear in the order F, C, G, D, A, E, B. A key with three sharps has F♯, C♯ and G♯, never any other three. A common English mnemonic is "Fat Cats Go Down Alleys Eating Birds." Flats come in the reverse order, B, E, A, D, G, C, F, so the two lists mirror each other. On the treble staff the sharps zigzag down and up, and the flats zigzag up and down, so you can often recognise a signature by its shape before reading every symbol.

Two quick tricks

For sharp keys, the last sharp is a half step below the tonic. Two sharps end on C♯, and a half step above C♯ is D, so the key is D major. Four sharps end on D♯, so the key is E major. For flat keys, the second-to-last flat names the tonic: three flats are B♭, E♭, A♭, and the second-to-last is E♭, so the key is E♭ major. Two keys do not fit the tricks and are simply memorised: C major has no sharps or flats, and F major has one flat, B♭.

The same tricks work backwards. For A major, the note a half step below A is G♯, so write sharps in order until you reach G♯: F♯, C♯, G♯, three sharps. For A♭ major, write flats in order until you pass A♭ by one: B♭, E♭, A♭, D♭, four flats. One more pattern helps: a key whose name has a flat uses flats, a key whose name has a sharp uses sharps, and natural-named keys other than C and F (G, D, A, E and B) are sharp keys.

Three keys sit at the extremes. C major has nothing, C♯ major has all seven sharps, and C♭ major has all seven flats. Counting none, one to seven sharps and one to seven flats gives 15 major key signatures in all. The 3D circle below shows each of them on a staff when you pick a key; try D major, then A major, and watch one sharp appear each time.