Perfect Fifth, Major Sixth, Minor Sixth, Major Seventh, Minor Seventh

Perfect Fifth: Named for the fifth note of the major scale. It’s an interval of seven semitones. It’s called “perfect” because, compared with the diminished fifth, it sounds a lot more “perfect” in the context of a chord or a tune. (But, as you’ll see, “perfect” doesn’t necessarily mean “interesting.” Just like people.)
Major Sixth and Minor Sixth: Named for the sixth note of the major scale. The major sixth is an interval of nine semitones. The minor sixth, one less at eight semitones.
Major Seventh and Minor Seventh: Named for the seventh note of the major scale. The major seventh is an interval of eleven semitones. The minor seventh is one less, at ten semitones.