Key signatures: why sharps arrive in that order

A key signature is the row of sharps or flats at the start of a line of music. It is a labour-saving device: rather than mark every F sharp in the piece, you say once at the top that all the Fs are sharp.

The order is fixed, and it is not alphabetical

Sharps always appear in this order:

F, C, G, D, A, E, B

One sharp means F sharp. Two means F sharp and C sharp. Three adds G sharp. You never get a key signature with a C sharp but no F sharp.

Flats appear in exactly the reverse order:

B, E, A, D, G, C, F

Which spells BEAD and then GCF, and that is how most people remember it.

Where the order comes from

Look at the sharp order again: F, C, G, D, A, E, B. Each one is a fifth above the last. F up to C is a fifth, C up to G is a fifth, and so on.

• F to C
• C to G
• G to D

That is the whole secret. The keys themselves are also a chain of fifths, and each time you move up a fifth to a new key, the major scale pattern demands exactly one new sharp, and it is always the seventh note of the new key.

C major has none. Go up a fifth to G and you need F sharp. Up another fifth to D and you need C sharp as well. The order is not a convention somebody imposed, it is the order the sharps become necessary.

Lay that chain out in a ring and you have drawn the circle of fifths, which is the same fact in a shape you can point at.

Reading one at a glance

Two shortcuts cover almost every case you will meet.

Sharps: look at the last sharp in the signature and go up one semitone. Three sharps ends on G sharp, one semitone up is A, so it is A major.

Flats: look at the second-to-last flat. That is the key. Four flats are B, E, A, D, the second-to-last is A flat, so it is A flat major. Only one flat has to be memorised on its own, and that is F major.

The same signature means two keys

One sharp is G major. One sharp is also E minor. They use the same seven notes and differ only in which note feels like home.

• G major
• E minor

The relative minor always sits three semitones below the major, and a piece usually tells you which one it is in by where it stops. If the last chord is G, it is G major. If it is E minor, it is E minor. Not subtle, but reliable.

Instruments that have no choice

All of this assumes an instrument that can play any note. Plenty cannot. A kalimba is a plain major scale in one key with no sharps at all, and a handpan is tuned to a single scale permanently, hammered into the steel. On those, a key signature is not a piece of information you read at the top of a page, it is a property of the object in your hands.