Name the big distance

The wider leaps, read from the keys. A perfect 4th is five semitones; a major 6th nine; a minor 7th ten; a major 7th eleven.

The octave is your ruler here: a major 7th falls one semitone short of it, a minor 7th two. A major 6th is one whole tone above the 5th you already recognise.

P4 = 5 · M6 = 9 · m7 = 10 · M7 = 11 semitones

One semitone short of the octave: a major 7th.

Practise this in the trainer — it opens with this lesson the first time the concept comes up.