Guide
How to make a sudoku book that has exactly one solution per puzzle
One bad puzzle destroys a sudoku book. A grid with two solutions, or none, gets found within a week of publication and sits in the reviews forever. Everything else in this guide is craft; uniqueness is the part you cannot get wrong.
Short answer
Generate a full solved grid, then remove clues one at a time and check after every removal that exactly one solution remains. Stop when the next removal would break uniqueness or when you hit your difficulty target. Ship 100 to 200 puzzles graded in four bands, keep the clue pattern rotationally symmetric, and print answers compactly in the back.
Uniqueness is the whole job
Sudoku has one rule beyond the grid itself: there must be exactly one way to complete it. A solver works by elimination, and elimination is only sound if no branch point exists. The moment a puzzle admits two answers, a careful solver hits a wall where logic gives out and guessing begins, and they know they have been sold something broken.
The safe construction order is always the same:
- Build a complete solved grid by filling the 81 cells with a backtracking search, randomised so every book is different.
- Remove one clue. Pick a filled cell, empty it, and its symmetric partner with it.
- Count the solutions. Run a solver that keeps going after it finds the first answer. If it finds two, put the clues back and try a different cell.
- Repeat until no further removal keeps uniqueness, or until you reach the clue count your difficulty band wants.
The expensive step is the third, and it is the one people skip. A generator that digs holes without counting solutions produces puzzles that look right and are not. There is no way to check by eye.
The floor is known: mathematicians proved in 2012, by exhaustive computer search, that no 16-clue sudoku has a unique solution. Seventeen is the minimum, and 17-clue puzzles are rare and very hard. Nothing in a commercial book needs to go near that.
Difficulty is about technique, not clue count
A puzzle with 30 clues can be harder than one with 24. What decides difficulty is which solving techniques a human must reach for.
| Band | Techniques needed | Typical clues | Share of the book |
|---|---|---|---|
| Easy | Naked and hidden singles only | 32 to 36 | 25 percent |
| Medium | Pairs, pointing pairs, box-line reduction | 28 to 32 | 35 percent |
| Hard | Triples, X-wing | 24 to 28 | 30 percent |
| Expert | Chains, colouring, trial branches | 22 to 26 | 10 percent |
Grade by simulation: run a solver that is only allowed the easy techniques and see whether it finishes. If it does, the puzzle is easy no matter how few clues it has. Label the bands in the book and group them in order. Solvers pick a band and stay in it; a book that mixes them at random feels arbitrary.
The page
A sudoku grid wants to be square, generous and plain. Heavy rules every three cells, light rules elsewhere, clue digits distinctly darker than anything the solver will write. Leave the pencil-mark corners empty and unlined: solvers put their own candidates there and a printed grid of tiny boxes gets in the way.
One puzzle per page for a large-print book, two for a standard one, four for a pocket edition. Number every puzzle and print the number in the same place on every page, because the answer key is useless otherwise.
All of this is line work, which means it should be drawn as vector rather than rendered as an image. A drawn grid stays crisp at any trim size and satisfies the 300 DPI requirement by construction, since there are no pixels to count.
Answers, and how to fit them
Solutions go in the back, six or eight to a page at reduced size, each with its puzzle number. Nobody reads an answer grid for pleasure, so it can be small; it just has to be unambiguous. Do not put the answer on the reverse of the puzzle page, where it shows through thin paper.
Publishing
Sudoku is a crowded category on Amazon, which means the cover and the promise do the selling. "200 sudoku puzzles" is invisible. "200 sudoku, large print, four difficulty levels, answers in the back, one puzzle per page" is a specification a buyer can compare. Say the clue counts. Say the grid size in points. The buyers in this category are specific people who have been let down before.
Follow the KDP paperback specification: PDF interior, minimum 24 pages, even page count, no bleed needed. A printable PDF edition on Etsy sells to the same people who buy puzzle packs for care homes and waiting rooms, under Etsy's download fees.
Neubook digs every sudoku symmetrically and counts the solutions after each removal, so a puzzle only ships when exactly one answer exists. Choose how many, pick your difficulty spread, and print the set.
Start a set, freeSources
- Sudoku
- The mathematics of sudoku, including the 17-clue minimum
- Amazon KDP paperback submission guidelines
- Etsy seller fees and payment policy
- Dots per inch, and why it decides print quality
- SVG, the vector format these pages are drawn in
Common questions
What makes a sudoku puzzle valid?
Exactly one solution. A grid with two or more valid completions is not a sudoku, it is a guessing game, and solvers notice immediately because logic stops working partway through. The only safe way to produce one is to check for uniqueness after every clue you remove.
How many clues does a sudoku need?
It has been proven that no sudoku with 16 or fewer clues can have a unique solution, so 17 is the floor. In practice, published puzzles run from about 22 clues at the hard end to 36 at the easy end. Clue count correlates with difficulty but does not define it.
How is sudoku difficulty measured?
By the solving techniques required, not by clue count. A puzzle solvable with singles alone is easy; one needing pairs and pointing is medium; one requiring chains is hard. Grade by running a solver that only knows certain techniques and seeing whether it finishes.
Why are the clues arranged symmetrically?
Convention, and it looks deliberate rather than accidental. Most published sudoku use 180-degree rotational symmetry: if a cell holds a clue, so does the cell diametrically opposite. It costs nothing and readers register the difference.
How many puzzles should a sudoku book have?
A hundred to two hundred, which is roughly what a buyer expects for the price. Sudoku pages are small, so four to a page for answers and one per page for puzzles gives a book of comfortable thickness without a punishing print cost.