interval
A♭ perfect fourth
A♭lowerD♭upperP45 half steps
Five half steps. Turned upside down it becomes a perfect fifth.
On the keyboard
What is true of it
A♭ up a perfect fourth is D♭: 5 half steps, and 4 letters counting both ends.
Turn it upside down — put the A♭ on top — and it becomes a perfect fifth. The two numbers always add to nine, and the two sizes to twelve.
It is a perfect consonance.
Every interval on A♭
A♭ → B♭♭minor second · dissonanceA♭ → B♭major second · dissonanceA♭ → C♭minor third · imperfect consonanceA♭ → Cmajor third · imperfect consonanceA♭ → Daugmented fourth · dissonanceA♭ → E♭♭diminished fifth · dissonanceA♭ → E♭perfect fifth · perfect consonanceA♭ → F♭minor sixth · imperfect consonanceA♭ → Fmajor sixth · imperfect consonanceA♭ → G♭minor seventh · dissonanceA♭ → Gmajor seventh · dissonance