C-sharp major (or the key of C-sharp) is a major scale based on C♯, consisting of the pitches C♯, D♯, E♯, F♯, G♯, A♯, and B♯. It is enharmonically equivalent to D-flat major. Its key signature has seven sharps.
|Relative key||A-sharp minor|
enharmonic: B-flat minor
|Parallel key||C-sharp minor|
|Dominant key||G-sharp major|
enharmonic: A-flat major
enharmonic: G-flat major
|C♯, D♯, E♯, F♯, G♯, A♯, B♯|
The C-sharp major scale is:
A harp tuned to C-sharp major has all its pedals in the bottom position. Because all the strings are then pinched and shortened, this is the least resonant key for the instrument.
Most composers prefer to use the enharmonic equivalent D-flat major, since it only contains five flats as opposed to C-sharp major's seven sharps. Johann Sebastian Bach chose C-sharp major for Prelude and Fugue No. 3 in both books of The Well-Tempered Clavier, and Charles-Valentin Alkan chose C-sharp major for Etude Op. 35 No. 9 "Contrapunctus" in Twelve etudes in all the major keys, Op. 35. In Hungarian Rhapsody No. 6, Franz Liszt takes the unusual step of changing key from D-flat major to C-sharp major near the beginning of the piece, and then soon back again to D-flat major. Maurice Ravel selected C-sharp major as the tonic key of "Ondine" from his piano suite Gaspard de la nuit. Erich Wolfgang Korngold composed his Piano Concerto for the Left Hand, Op. 17, in the key of C-sharp major.
In a few scores, 7-sharp key signatures in the bass clef are written with the sharp either for the A or for the A and the B on the top line.
Canadian composer and pianist Frank Mills originally wrote and performed his instrumental hit "Music Box Dancer" in C-sharp major. However, most modern piano editions have the song written in the Key of C.