The Perfect 5th

7 semitones — stable and open

Prove it — just do the practice exercise.
C → G 7 semitones
C (root) G (P5)
The perfect 5th = 7 semitones:

• Sounds open and stable
• Foundation for power chords (rock)
• Often dropped in shell voicings — because it doesn't define the character

Example: C → G = perfect 5th

The circle of fifths is based on this interval — each key is one fifth from the next.