Don't be a mug, get a ... wait, did we already do that joke?
After a hard day's witching, you'll often find yourself needing a wee aperitif. In that case (or a number of more likely cases), you'll be wanting this generous-capacity mug.
The mug is 14.5cm tall, so if your shelves are 14cm apart, it won't fit unless you put it on its side. A 15cm-spaced shelf should be fine.