← Music Theory · Scales & keys · about 20 min
Key signatures & the circle of fifths
How to know a song's sharps and flats at a glance.
What is a key signature?
A key signature is a set of sharps or flats written at the start of every line of music. It saves writing the same sharp or flat over and over.
If you see one sharp (F♯), the song is probably in G major. No sharps or flats usually means C major.
The circle of fifths
The circle of fifths is a map of all twelve major keys. Starting at the top with C, each step clockwise adds one sharp. Each step counterclockwise adds one flat.
So G has one sharp, D has two, A has three, and so on. F has one flat, B♭ has two, E♭ has three.