The number of pages in "Middle World" can vary depending on the edition and format of the book. Typically, the book has around 300-400 pages.
Tolkien's World from A to Z: The Complete Guide to Middle-Earth is by Robert Foster. It has 569 pages. The mass market book A Guide to Middle Earth is also by Robert Foster. It has 283 pages.
The Pagan Middle Ages has 160 pages.
The Middle Years - story - has 11 pages.
The One in the Middle Is the Green Kangaroo has 39 pages.
The Middle Age of Mrs Eliot has 430 pages.
The Complete Guide to Middle-earth has 573 pages.
The Holder of the World has 286 pages.
Terminal World has 487 pages.
Learning the World has 303 pages.
The Birthday of the World has 362 pages.
Empress of the World has 213 pages.
The Drowned World has 158 pages.