Hogwarts: How Big?
Neil Ward

Just how big is Hogwarts castle? If the Entrance Hall is big enough to hold an entire house, and the Great Hall is even bigger, it must be vast indeed. On the other hand, Harry encounters crowds in the corridors, which suggests that the students fill the space inside, and that certainly suggests a fairly cozy place, even if you accept a student count of about a thousand (and evidence suggests that there are far less students than that). Neil Ward, on HP4GU, tackled that question. He says:

"Hogwarts, in my view, is a castle that has the ability to change its size, shape and room-arrangement according to need:
 

"There were a hundred and forty-two staircases at Hogwarts: wide, sweeping ones; narrow, rickety ones; some that led somewhere different on a  Friday...and doors that weren't really doors at all, but solid walls just pretending. It was also very hard to remember where anything was, because it all seemed to move around a lot...." (SS8)

Perhaps areas that aren't used or that house smaller numbers of people are
contracted to a smaller size, sealed off (like the Chamber of Secrets) or
made 'invisible'.  This would make the Marauder's Map seem even more incredible, of course, but is perhaps the reason for needing a map in the first place. It could also be that Filch, having no magical ability, needs Mrs Norris to direct him around the castle, which would, otherwise, confuse him; in other
words, from a magical perspective, Filch is 'blind' and Mrs Norris is his
guide-cat.

We know that Diagon Alley, for example, can co-exist with the Muggle
world, and there is a Muggle Hogwarts - a fixed, 'ruined' castle - and a
magical Hogwarts, which is, perhaps, sentient (like a computer, with some functional hardware, some variable 'memory' locations and the ability to create virtual environments).  I'd suggest that some of the rooms are part
of the Muggle structure and some, like Dumbledore's office or the room where
the Mirror of Erised was stored or the room full of chamberpots, are in a
parallel, magical plane, which appear when required.

Now the only question is, where does the Castle keep its brain? If we
can't see where it keeps it, we're in trouble.

copyright 2001 Neil Ward