Page Table Size Calculator: Address Bits, Levels and Table Size

How to use the Page Table Size and Address Bits Calculator

1. 1. Enter the sizesType the virtual address bits, page size and either the page table entry size or the physical memory size.
2. 2. Choose levelsLeave it on auto so each table fits in one page, or fix the number of levels.
3. 3. Check the extrasAdd a process size to see the memory its tables need, or a hex address to split into fields.

The formulas

• Offset bits = log₂(page size).
• Page number bits = virtual address bits − offset bits. Pages = 2^{page number bits}.
• Frames = physical memory ÷ page size; frame bits = log₂(frames).
• Single-level page table = pages × entry size.
• For multi-level paging, one page holds page size ÷ entry size entries, so each level indexes log₂ of that many bits. Levels = ⌈page number bits ÷ bits per level⌉.

Worked example

32-bit logical addresses, 4 KB pages, 4-byte entries.

• Offset = log₂ 4096 = 12 bits, page number = 32 − 12 = 20 bits.
• Single-level table = 2²⁰ × 4 B = 4 MB for every process.
• One page holds 4096 ÷ 4 = 1024 entries, so each level takes 10 bits: the format is 10 | 10 | 12.

An 8 MB process uses 2048 pages, so it needs 2 inner tables and 1 outer table: 3 × 4 KB = 12 KB instead of 4 MB. With 48-bit addresses and 8-byte entries, a page holds 512 entries (9 bits), giving the familiar 4-level 9 | 9 | 9 | 9 | 12 format.

When the entry size is not given

Work it out from the frame number plus any extra bits (valid, dirty, protection), rounded up to whole bytes. With 1 GB of memory and 4 KB pages there are 2¹⁸ frames, so 18 bits + 2 extra bits = 20 bits, stored in 3 bytes. Check whether your question wants it rounded to bytes or to a power of 2.

Frequently asked questions

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