Key Signature Calculation

A key signature is the group of sharps or flats written at the start of every staff, right after the clef. It tells you which notes are raised or lowered throughout the piece. Instead of memorising all fifteen key signatures, you can work them out with a few quick tricks.

The order of sharps and flats

Sharps and flats always appear in a fixed order. Learn these two sequences and half the work is done.

• Order of sharps: F C G D A E B, remembered as "Father Charles Goes Down And Ends Battle".
• Order of flats: the exact reverse, B E A D G C F, remembered as "Battle Ends And Down Goes Charles' Father".

A key signature never skips ahead: two sharps are always F and C, three flats are always B, E, and A, and so on.

Finding the major key from sharps

The last sharp in the signature is the leading tone, the note one half step below the tonic. So the major key sits a half step above the last sharp.

1. Read the sharps in order and find the last one.
2. Go up a half step from that note.
3. That note names the major key.

With three sharps (F#, C#, G#), the last sharp is G#. A half step above G# is A, so the key is A major.

Finding the major key from flats

Flats are even easier: the second-to-last flat is the name of the major key.

1. Read the flats in order.
2. Look at the one just before the last.
3. That flat names the major key.

With three flats (B♭, E♭, A♭), the second-to-last is E♭, so the key is E♭ major. The one exception is a single flat (B♭), which is F major. That one is worth memorising.

Going the other way, and relative minors

To find the signature from a key name, use the circle of fifths or count outward. Every major key also shares its signature with a relative minor, whose tonic is a minor third (three half steps) below the major tonic. A major and F# minor use the same three sharps.

The circle of fifths ties all of this together: each step clockwise adds a sharp, each step counter-clockwise adds a flat. Spin the interactive circle below to check your answers.