Key signatures for all 12 keys

Concept

Each spot on the circle tells you exactly which sharps or flats that key uses. Sharps appear in this order: F# C# G# D# A# E# B#. Flats are the reverse: Bb Eb Ab Db Gb Cb Fb. So G major has 1 sharp (F#). D major has 2 (F#, C#). And so on, adding one each step.