interval
C♯ perfect fifth
C♯lowerG♯upperP57 half steps
Seven half steps. Stack twelve of them and you land back where you started, give or take a comma.
On the keyboard
What is true of it
C♯ up a perfect fifth is G♯: 7 half steps, and 5 letters counting both ends.
Turn it upside down — put the C♯ on top — and it becomes a perfect fourth. The two numbers always add to nine, and the two sizes to twelve.
It is a perfect consonance.
Every interval on C♯
C♯ → Dminor second · dissonanceC♯ → D♯major second · dissonanceC♯ → Eminor third · imperfect consonanceC♯ → E♯major third · imperfect consonanceC♯ → F♯perfect fourth · perfect consonanceC♯ → F𝄪augmented fourth · dissonanceC♯ → Gdiminished fifth · dissonanceC♯ → Aminor sixth · imperfect consonanceC♯ → A♯major sixth · imperfect consonanceC♯ → Bminor seventh · dissonanceC♯ → B♯major seventh · dissonance