C♯ major has 7 sharps — F♯, C♯, G♯, D♯, A♯, E♯, B♯. Here's the signature on the staff, the full scale, its relative minor, and the trick to recognize it instantly.
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The fastest way to spot a sharp key is the last sharp: it always sits a semitone below the tonic. C♯ major's final sharp is B♯, and a semitone above that is C♯ — the key. Count 7 sharps and you have C♯ major every time.
The C♯ major scale runs C♯, D♯, E♯, F♯, G♯, A♯, B♯. Every sharpened note in the piece takes the key's accidentals automatically, which is exactly what the signature saves you from writing note by note.
C♯ major shares its signature — 7 sharps — with its relative minor, A♯ minor, a minor third below the tonic. They use the same seven pitches; what tells them apart is which note the music settles on and treats as home.
Neighboring keys on the circle of fifths
C♯ major has 7 sharps — F♯, C♯, G♯, D♯, A♯, E♯, B♯.
The relative minor of C♯ major is A♯ minor — it shares the identical key signature (7 sharps).
The C♯ major scale is C♯, D♯, E♯, F♯, G♯, A♯, B♯.
Keep practicing: key signature quiz · circle of fifths · key trainer
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