Sudoku Made and maintained by Brian Hamilton and Karan Hamilton.
Brian builds the playable puzzle tools, while Karan helps test clarity, difficulty feel, and the player experience.
Playable puzzles and controls are tested in the browser for rule accuracy, usability, and a clear solving experience. See how we make and test puzzles, our editorial standards, or report a problem.
What is 12×12 Sudoku?
12×12 Sudoku is sudoku on a larger board: 144 squares and the digits 1 to 12. Fill the grid so that every row, every column and every box holds each digit once. The part worth understanding first is the box. Twelve has no whole-number square root, so the boxes cannot be square: they are 3 rows tall and 4 columns wide, and the grid is three boxes across and four boxes down.
- A row passes through 3 boxes, taking 4 squares from each.
- A column passes through 4 boxes, taking 3 squares from each.
On a 9×9 board those two sentences are the same. Here they are not, and every step that has a box meeting a line inherits the difference.
Each of 10, 11 and 12 fills one square, like any other digit. From a keyboard, type 0 for 10, the minus key or Q for 11, and the equals key or W for 12. In a dense field of pencil marks 11 and 12 are the easiest pair to mix up, so glance at the row once whenever you write one.
What does the 3×4 box change?
Ask where a digit can go inside one box. The box has only three rows, so once the digit sits in two of the rows crossing it, it is pinned to the third; it has four columns, so pinning it to one column takes three. Cross-hatch along rows first. When the rows and columns together leave a digit one square in a box, that square is the digit, whatever else its pencil marks say:
That is a hidden single, and on Easy and Medium boards here it is all you need, together with naked singles: every one of those boards is dug so that singles alone finish it.
What do you do when singles run out?
On Hard and Expert they do. The first step past them is usually locked candidates: when a digit’s places in a box all lie in one row or one column, it comes out of the rest of that line.
The box shape pays out unevenly here too. A digit locked to one row inside a box clears the other 8 squares of that row; locked to one column, it clears 9, because the box takes only 3 squares of a column. Column locks are harder to spot and reach further when you find them.
Were the boards on this page fair?
For the page’s first thirteen days, from 31 March 2026, the generator checked nothing, and all 160 boards we dealt from that first version have more than one answer. From 13 April every board had exactly one answer; the old generator checked that properly from then on. What it did not do was finish in reasonable time, or deal the levels it promised. It tested every digit against every square around it at every step, with no shortcuts, so an Easy board took up to 1.5 seconds to appear, a Medium board a median of 17 seconds and up to 81, and Hard and Expert boards around 20 seconds each — one Hard board in our sample took seven minutes.
And the levels were not the levels they said. A random dig on a 12×12 stalls at about 45 to 51 givens, so Medium, Hard and Expert all came out with about the same number of digits, never the 38 and 32 promised for Hard and Expert. At 55 givens, only 10 of 40 Easy boards could be finished with singles, and 21 went beyond everything our solver knows. The generator now uses the same fast engine as the rest of the site, and deals any level in at most about a tenth of a second.
How do the four levels differ?
Easy and Medium are dug with a rule: a digit comes out only while naked and hidden singles can still finish the board. Hard and Expert only have to keep one answer. We ran 40 fresh boards per level through a solver that knows one technique at a time.
| Level | Given digits | How it is dug | Singles finish it | Beyond our solver |
|---|---|---|---|---|
| Easy | 60 | singles must finish it | 100% | 0% |
| Medium | 45–52 | singles must finish it | 100% | 0% |
| Hard | 57 | one answer | 43% | 38% |
| Expert | 45–51 | one answer | 0% | 90% |
40 boards per level from this page’s generator, fixed seed; shares rounded. Medium and Expert dig as far as their rule allows, a median of 48 and 47 givens. The solver knows naked and hidden singles, locked candidates, naked pairs and triples, and the X-Wing; “beyond our solver” boards still have exactly one answer.
Hard gives more digits than Medium, and is still harder. Medium’s digits are chosen so singles always finish the board; Hard’s are not, and on 23 of its 40 boards singles stall somewhere. Expert is the real wall: not one of its boards falls to singles, and 36 of 40 go beyond everything our solver knows. Every one of them has exactly one answer.
On Easy and Medium the proof is the rule itself: if singles can finish a board, it has only one answer. On Hard and Expert every removal is checked with a search for a second answer; a search that runs out answers “not proven” and the digit stays. We re-solved 160 fresh boards with a separate counter written for the purpose: every one had exactly one answer. The deepest check took 809 search steps of the 4,000 it is allowed.
Which level should you play?
Start on Easy, even if 9×9 is easy for you. It teaches the 3×4 rhythm — rows first, then columns — with nothing harder than singles. Medium is the same skill with fewer digits and a longer board, still never beyond singles.
Hard is where you need more than singles on more than half the boards, often just locked candidates. Expert is for solvers who already know pairs, triples and beyond: nine boards in ten need something our solver does not have.
A solving order that works here
- Open with the fullest boxes. A box holding six or more givens is usually where the first placements are.
- Scan rows before columns. A box has three rows but four columns, so row cross-hatching pins a digit sooner.
- Fill notes a band at a time. The three boxes side by side in one horizontal strip make a closed region to reason about.
- Sweep one digit at a time. Pick a digit, find every square it can still take across the board, and place what resolves.
- Re-check a surprising move. On a board this long, a surprise is more often an earlier slip than a clever pattern.
What do the buttons do?
Select a square, then a digit from 1 to 12; the page opens on Easy. Selecting a square highlights its row, column and box, and a wrong digit is marked the moment it goes in. Under the grid:
- Notes turns pencil marks on and off. A correct digit clears itself from the notes of its row, its column and its box; a wrong one leaves your notes alone.
- Erase clears the selected square, and pressing the same digit twice does the same.
- Undo takes back the last change to a square, though not the notes a correct digit cleared elsewhere, and not the Mistakes count.
- Hint fills one square with its answer, picked at random rather than the square you could work out next.
- Solve asks first, then fills the grid and stops the timer.
- New Game deals another board at the level you are on; the level buttons deal one at theirs.
From a keyboard: 1–9, then 0 for 10, minus or Q for 11 and equals or W for 12; the arrow keys, Backspace or Delete and Ctrl+Z. The board is saved in this browser after every move, so it is waiting when you come back.
Where to go next
6×6 Sudoku uses the same rectangular idea in miniature, with 2×3 boxes, and is the quickest way to get the feel of it. 16×16 Sudoku goes back to square boxes at 4×4 on 256 squares, and Jigsaw Sudoku drops rectangles altogether. For a 12×12 on paper, there are PDFs at four levels on our printable 12×12 page, and more in the printable sudoku collection.