A Major 7th is equivalent to moving up 7 degrees in the major scale, starting on the tonic.
It is also equivalent to 11 semitones.
By themselves, their sound is somewhat harsh but can be quite beautiful when used as part of a chord.
Like other large intervals, it is best to find an anchor point, rather than counting through all seven degrees of the scale.
In this case, go up an Octave, then down a half step.