Re: How Big is the Eye of Harmony? (spoilers Journey to the center TAR
As the interior is apparently created/maintained by the TARDIS herself, it seems sensible that while its potentially infinite, to make it actually infinite would require an infinite amount of energy. And an infinite amount of energy to maintain.
"Some days are better than others. They say that where I come from."
"Loudly, I imagine, on the day you left."
(Blake's 7 - Rumours of Death)