What is the interval quality between C and G?

• A. Diminished fifth
• B. Perfect fifth
• C. Perfect fourth
• D. Augmented fifth

Answer: (B)

Interval quality is decided by both the span in letter names and the exact number of semitones between the two pitches. From C up to G, you move through C–D–E–F–G, which is five letter names, so the interval is a fifth. Counting semitones, C to G covers seven steps: C–C# (1), C#–D (2), D–D# (3), D#–E (4), E–F (5), F–F# (6), F#–G (7). A fifth that consists of seven semitones is called a perfect fifth. If the semitone count were different—six for a diminished fifth, eight for an augmented fifth, or five for a perfect fourth—the quality would change accordingly. Therefore, the interval from C to G is a perfect fifth.