A machine has a 32-bit address space and an 4-KB page. Suppose a simple OS just boot up on the machine, running a single process. The process uses 2 memory pages for the text and data memory (combined) near the lowest virtual address, and 1 memory page for the stack memory near the highest virtual address.
Suppose each page table or page directory entry is 8 bytes. A single-level page table would require KB of memory; a 2-level page table, with address bits for the virtual page number equally divided by the two levels, would require at least KB of memory and at most KB of memory.
(Note: 1KB = 1024 bytes)