interval
B perfect fifth
BlowerF♯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
B up a perfect fifth is F♯: 7 half steps, and 5 letters counting both ends.
Turn it upside down — put the B 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 B
B → Cminor second · dissonanceB → C♯major second · dissonanceB → Dminor third · imperfect consonanceB → D♯major third · imperfect consonanceB → Eperfect fourth · perfect consonanceB → E♯augmented fourth · dissonanceB → Fdiminished fifth · dissonanceB → Gminor sixth · imperfect consonanceB → G♯major sixth · imperfect consonanceB → Aminor seventh · dissonanceB → A♯major seventh · dissonance