OK, to put the wooden spoon of pedantry in the murky bowl of musical porridge, and give it a good stir, there are three types of fifth. The Perfect Fifth, which is 7 semitones above the tonic, the Augmented Fifth which is 8 semitones above the tonic or starting note and the Diminished or flattened Fifth which is 6 semitones above the original note.

NOTE Diatonically means using only the notes in the scale.

We think of the interval between note one of the scale and note five as the fifth interval, of course, but the interval between note two and note six is also a fifth. As is the interval between note three and note seven and so on and so on. These are all perfect fifths with one exception. The interval between note seven and the note four above it is a Diminished Fifth, 6 semitones. This is why, by the way, the chord formed diatonically on the seventh note of a major scale is always a Diminished Chord.

Add salt to your porridge to taste.