How the sudoku maker works
This page runs the sudoku generator kdpbook uses for its puzzle books, in your browser. It fills a random complete grid, then removes clues in pairs that mirror each other through the center, the classic rotational symmetry. After every removal a solver counts the solutions, and the pair goes back if the grid no longer has exactly one. It stops near the clue count of the level you chose.
On easy and medium, a clue only comes out if the grid can still be solved with naked and hidden singles: a cell with a single possible digit, or a digit with a single possible cell in its row, column or box. For hard and expert grids the generator tries several puzzles and keeps one that singles alone can’t finish when it finds one. The Solving figure above the preview tells you which you got.
Difficulty and number of clues
Target clues (given digits) per grid for each size and level. Fewer clues usually means a longer solve, but the techniques needed matter as much as the count.
| Grid | Easy | Medium | Hard | Expert |
|---|---|---|---|---|
| 4×4 · 2×2 boxes | 9 | 7 | 6 | 4 |
| 6×6 · 2×3 boxes | 18 | 15 | 12 | 10 |
| 9×9 · 3×3 boxes | 38 | 32 | 28 | 24 |
No standard 9×9 sudoku with fewer than 17 clues has a unique solution: Gary McGuire, Bastian Tugemann and Gilles Civario proved it in 2012 with an exhaustive computer search. The expert level here keeps about 24 clues, the easy level about 38.
Sudoku for kids, and several grids per page
4×4 grids use the digits 1 to 4 in 2×2 boxes, and 6×6 grids the digits 1 to 6 in 2×3 boxes (two rows by three columns): the same rules with far fewer cells, a good first step before 9×9. With 2, 4 or 6 grids per page, each grid gets a number, and the answer key repeats the layout with the clues shaded so every solution sits where its puzzle was.
From printable sudoku to a KDP sudoku book
A sudoku book is a regular paperback on KDP: KDP’s low-content category covers notebooks, planners and journals and does not typically include puzzle books, so the book needs an ISBN (KDP offers a free one) and at least 24 pages. Like the puzzle books, these pages keep every line at least 0.75 pt thick and every digit at 8 pt or larger, which meets KDP’s minimums of 0.75 pt for lines and 7 pt for text. This maker uses no AI model; if an AI tool drew your cover or wrote any text, KDP asks you to disclose that AI-generated content when you publish (see KDP AI content disclosure, explained).
For a whole book, kdpbook’s sudoku book type builds a 108-page 8.5 × 11 in interior of large-print sudoku that get harder through the book, with the solutions at the back, plus the full-wrap cover and the listing; the puzzle book type mixes sudoku with word searches and other puzzles. The default sudoku book is estimated at 460 credits. New accounts get 2,000 free credits once, with no card required. Free-plan books carry a kdpbook.io preview watermark and are shared in the community; any paid plan exports clean files. The word search maker and the maze maker print other puzzles the same way.