Giant Sudoku: A Guide to Every Oversized Grid

Giant sudoku means one of two completely different things: a classic 9x9 printed at large size for easier reading, or a puzzle on a board bigger than 9x9 — 12x12, 16x16, 25x25, or one of the multi-grid monsters that join several boards together. Both are sold under the same name, sometimes on the same website, and buying the wrong one is a common annoyance.

This page covers both meanings, lists every grid size that can legally exist and the box shape each one requires, sorts out the tangle of names (mega sudoku, monster sudoku, super sudoku, hexadoku), and explains what actually changes about solving when a grid gets large.

The two things "giant sudoku" means

One meaning is about print size. The other is about grid size. They have almost nothing in common.

Large-format sudoku is a standard 9x9 puzzle printed big — cells an inch or more across, thick borders, heavy type. The logic is identical to any newspaper sudoku. What changes is accessibility: it's the format used in large-print puzzle books, in care homes, in classrooms where a teacher works a grid on a whiteboard, and by anyone whose eyes have stopped enjoying 6-point pencil marks. Wall-poster and floor-mat versions exist too, some of them several feet across, for group solving.

Oversized-grid sudoku is a bigger board. More cells, more symbols, larger boxes, longer solve. This is what most people mean when they search the term, and it's the bulk of this guide.

If you're buying a book or downloading a pack, check which one you're getting. "Giant sudoku, 100 puzzles" tells you nothing on its own; look for either a stated grid size or a stated cell measurement.

Every legal giant sudoku size

A sudoku grid can only exist at sizes where the number of symbols factors into two whole numbers greater than one, because those two factors become the height and width of each box. That single rule generates the entire list.

Two things stand out. First, the sizes with square boxes — 16x16, 25x25, 36x36 — are the ones publishers favor, because square boxes make row logic and column logic behave identically and the grid looks right. Second, prime sizes are missing entirely. There is no 11x11, 13x13, or 17x17 sudoku, because a prime number of symbols cannot be split into equal rectangular boxes. The same problem is why a sudoku 5x5 can't have normal boxes either.

For rectangular-box sizes like 12x12, the orientation is a publisher's choice. Boxes 3 tall by 4 wide and boxes 4 tall by 3 wide are both correct, and they produce mirror-image puzzles. Trace the bold borders before your first move.

Mega sudoku, monster sudoku, super sudoku: the naming problem

These names have no agreed definitions, so treat all of them as "bigger than 9x9" and check the actual grid before you rely on the label. That's the honest answer, and it saves a lot of confusion.

The usage that's most common in practice:

• Mega sudoku — usually 16x16, but 12x12 and 25x25 both appear under the name. A few publishers use "mega sudoku" for any oversized grid whatsoever, and at least one uses it for the large-print 9x9.
• Monster sudoku — usually 16x16 or 25x25. Sometimes reserved for 25x25 and above.
• Super sudoku — usually 16x16, though some newspapers use it for a 9x9 with an extra constraint rather than a bigger board.
• Hexadoku — reliably 16x16 in hexadecimal. This is the one name that means what it says.
• Giant sudoku — the broadest term of the lot, covering everything on this page and the large-print format too.

If a product page says "mega sudoku" without a grid size, assume 16x16 and verify. The full treatment of that size lives on our play 16x16 sudoku online page.

A verified 12x12 grid

12x12 is the friendliest entry point into the big grids, because 12 symbols is a manageable jump from 9 and the boxes are only slightly unfamiliar. Here is a complete, valid 12x12 solution using boxes 3 rows tall and 4 columns wide. Box borders fall after rows 3, 6, and 9, and after columns 4 and 8.

`` 3 5 6 2 | 8 10 9 7 | 12 11 4 1 8 9 7 10 | 12 4 1 11 | 3 6 2 5 12 1 11 4 | 3 2 5 6 | 8 7 10 9 ------------+-------------+------------ 1 11 2 12 | 5 3 6 10 | 9 4 8 7 9 7 4 8 | 1 12 11 2 | 5 10 3 6 5 6 10 3 | 9 8 7 4 | 1 2 12 11 ------------+-------------+------------ 2 3 5 11 | 10 6 8 9 | 4 1 7 12 10 8 9 6 | 4 7 12 1 | 2 5 11 3 4 12 1 7 | 2 11 3 5 | 10 9 6 8 ------------+-------------+------------ 6 10 8 5 | 7 9 4 12 | 11 3 1 2 7 4 12 9 | 11 1 2 3 | 6 8 5 10 11 2 3 1 | 6 5 10 8 | 7 12 9 4 ``

Check the top-left box: 3, 5, 6, 2, 8, 9, 7, 10, 12, 1, 11, 4 — all twelve, no repeats. Column 1 reads 3, 8, 12, 1, 9, 5, 2, 10, 4, 6, 7, 11 — also complete.

Notice what the rectangular box does to your solving. Each box covers four columns but only three rows, so a column elimination removes a third of a box's cells while a row elimination removes a quarter. Crosshatching down columns is more productive than crosshatching across rows on this layout, and the reverse is true if your puzzle uses 4-tall boxes.

Overlapping giants: Samurai and friends

A second family of big puzzles joins several complete 9x9 grids so that they share boxes, and the shared cells must satisfy both grids at once. These are called Gattai puzzles, from the Japanese for "joined."

The best known is Samurai sudoku: five 9x9 grids, with four of them positioned at the corners of a central grid so that each corner grid shares one 3x3 box with the center. Five grids of 81 cells would be 405, but four boxes of 9 cells are shared, so the real total is 369 cells.

Publishers vary in what they call these arrangements, and a few names are used for more than one layout, so read the picture rather than the label.

The solving experience is genuinely different. Overlapping regions are where the puzzle lives: a shared box gets constraint information from two grids simultaneously, which makes it far more determined than any box in a standalone puzzle. The standard advice is to work the overlaps first, ride the extra information as far as it goes, and only then treat each grid separately. Corner grids in a Samurai are often nearly unsolvable in isolation and nearly free once the shared box resolves.

What actually changes when a grid gets big

Bigger grids are longer rather than deeper — the techniques are the same, but the bookkeeping grows faster than the difficulty. That's the single most useful thing to understand before starting one.

Here's the mechanism. On a 9x9, each cell has 20 peers out of 80 — a quarter of the board reacts to every placement. On a 25x25 with 5x5 boxes, each cell has 24 row peers, 24 column peers, and 16 more inside its box that aren't already counted, for 64 peers out of 624. That's about 10%. The same placement does proportionally less work, so the satisfying cascade that finishes a 9x9 never quite arrives.

The consequences:

• Candidate lists become mandatory. You can finish a 9x9 without writing a single pencil mark. You cannot do that on a 25x25.
• Crosshatch by frequency, not by symbol order. On a giant grid, start with whichever symbol already appears most often among the givens. It will resolve several more immediately, and each of those makes the next symbol easier.
• Locked candidates get more valuable. Confining a symbol to one row within a box eliminates it from far more cells on a big grid than on a small one. These are the highest-yield deductions available.
• Errors get much more expensive. A mistake on move 40 of a 600-cell puzzle may not surface until move 300. Take a snapshot after the first full candidate pass.
• Difficulty ratings mean less. An "easy" 25x25 is easy in the sense that each step is simple, and hard in the sense that there are two thousand of them.

None of this makes the big grids less enjoyable. It makes it a different kind of enjoyable — closer to a long, absorbing project than a coffee-break puzzle.

Choosing a size

Match the grid to how much time you want to spend, because that's the variable that actually changes.

For the largest sizes, print rather than solve on screen if you can — scrolling a 36x36 grid in a browser window loses the whole-board view that makes pattern spotting possible.

Other variants to try

If size isn't the axis you want to push, extra rules are the other direction.

• Hyper sudoku — a 9x9 with four extra shaded 3x3 regions. More constraint on the same familiar board.
• Killer sudoku — cage sums replace most of the starting clues.
• Colored sudoku — colors instead of digits, which some solvers find far easier to scan on large grids.
• 6x6 sudoku — the opposite extreme, and the fastest crosshatching drill available.
• Sudoku 5x5 — why prime-sized boards can't work the way you'd expect.
• Sudoku evil — 9x9 at the top of the difficulty scale, if you want harder rather than longer.

For printable classic grids, our free puzzle maker generates 9x9 sudoku at easy, medium, and hard, one to six per page, with an answer key on every sheet.

Frequently asked questions

What size is a giant sudoku?

There's no fixed size, which is the frustrating part. The label is applied to 12x12, 16x16, 20x20, 25x25, and 36x36 grids, to multi-grid Samurai puzzles, and separately to large-print 9x9 puzzles that aren't oversized at all. Always check for a stated grid dimension before buying or printing a pack.

Is mega sudoku the same as giant sudoku?

Usually but not reliably. "Mega sudoku" most often means 16x16, while the giant label is the broader umbrella. Since neither term is standardized, two publishers can use them in opposite ways. The only dependable name in this family is hexadoku, which always means a 16x16 in hexadecimal.

Why is there no 11x11 or 13x13 sudoku?

Because 11 and 13 are prime. A sudoku box has to be a rectangle whose height times width equals the number of symbols, and a prime number only factors as 1 times itself — which gives you a box the shape of a single row or column, and those are already constrained. Every legal sudoku grid size is a composite number.

How many cells does a Samurai sudoku have?

1. Five 9x9 grids would be 405 cells, but the four corner grids each share one 3x3 box with the central grid, so 36 cells are counted twice. Subtracting them leaves 369 distinct cells to fill.

Are big grids harder than normal ones?

Longer rather than harder, at equivalent difficulty ratings. No new technique is needed — rows, columns, boxes, singles, locked candidates, and subsets are the whole toolkit at any size. What grows is the amount of scanning and record-keeping, which is why organization matters more than cleverness on a big grid.

Do I need special notation for large grids?

Not special, but disciplined. Number your rows and columns in the margins, because "the fourth cell from the left in the ninth row" is unusable on a 25x25. Use a consistent character shape for symbols that look alike — handwritten B and 8, or 0 and D, cause more failed hexadoku attempts than any logical difficulty does.