In music theory, an augmented sixth is an interval that has ten half steps 
The augmented sixth requires that:
- The interval must be a sixth interval (six note names between the first and the last).
- The interval must have ten half steps.
What does an augmented sixth look like?
Here is an example of a melodic augmented sixth (two music notes in a melody) and a harmonic augmented sixth (in a chord):
How to recognize an augmented sixth?
Rule of music theory: All intervals in a major scale starting with the tonic (degree I) are either major or perfect, and only unison, octave, fourth and fifth are perfect (the others are major).
Example with the interval D♭ / B♮:
Let's take the D flat major scale to have D♭ as the tonic:
From the rule stated above, the interval D♭ / B♭ is a major sixth so the interval D♭ / B♮ is an augmented sixth.
Inversion of the augmented sixth
The inversion of the augmented sixth is the diminished third.
Here is an example of a diminished third:
Musical examples of augmented sixth
No examples yet, but feel free to send me some examples!
Interval identification game
You will find this interval in my Intervals identification game: