  The 'popcorn function' isThe `popcorn function' is a well-known and important
example in real analysis with many interesting features. We prove that the box
dimension of the graph of the popcorn function is 4/3, as well as computing the
Assouad dimension and Assouad spectrum. The main ingredients include
Duffin-Schaeffer type estimates from Diophantine approximation and the
Chung-Erd\H{o}s inequality from probability theory.
