Count four letters

C, D, E, F make four note letters. C–F and C–F♯ are both fourths; the sharp changes the distance.

Five or six semitones

C–F is a perfect fourth (P4) at five semitones. C–F♯ is an augmented fourth (A4) at six. Six semitones are three whole tones, so A4 is a tritone. C–G♭ reaches the same key but is spelled as a diminished fifth.

Practice the relationship

Start on different roots, compare five and six steps, then locate the target from P4 or A4.