Sudoku Generator — Create Printable Sudoku Puzzles
Generate valid Sudoku puzzles with customizable difficulty levels. Print puzzles for offline solving or share them with friends. 100% client-side — puzzles are generated in your browser.
What makes a Sudoku puzzle valid? A valid Sudoku is a 9×9 grid in which every row, every column and each of the nine 3×3 boxes contains the digits 1 to 9 exactly once, and which has exactly one solution reachable by logic alone. Uniqueness is the part that matters: a grid with two possible completions is not a Sudoku, because solving it would require a guess that cannot be justified.
How to Use the Sudoku Generator
- Choose a difficulty — The setting controls how many cells are left blank, from 35–40 on Easy up to 50–55 on Expert. Fewer given numbers generally means a longer chain of deductions before the grid opens up.
- Set how many puzzles you want — Anything from 1 to 10 in a single batch. Each one is generated independently, so no two grids in a batch are the same.
- Decide whether to include solutions — Leave Include Solution ticked to print the answer grid under each puzzle, or clear it when you are handing the sheet to someone else.
- Switch on printable format if you are printing — Printable Format strips the interface styling and lays the grids out for paper before you send them to the printer.
- Press Generate — Each puzzle is built from a complete random grid and then thinned out, with the uniqueness of the solution rechecked after every removal.
- Print or copy the batch — Print opens the printer-ready view and Copy All puts every grid on the clipboard as plain text, which pastes cleanly into a document or a message.
How the Puzzles Are Generated
Building a Sudoku is a two-stage job: make a full grid, then take numbers away without destroying the single solution.
The first stage fills an empty 9×9 grid using backtracking. The algorithm walks cell by cell, tries the digits 1 to 9 in a shuffled order, and keeps any digit that does not already appear in that cell's row, column or 3×3 box. When a cell has no legal digit left, it steps back to the previous cell and tries the next option there. Shuffling the candidate order is what makes each run produce a different completed grid rather than the same one every time.
The second stage removes clues. Cells are visited in random order and blanked one at a time, but each removal is provisional: the partly emptied grid is re-solved by an exhaustive search that stops as soon as it finds a second solution. If two solutions exist, the number is put straight back and the next cell is tried. Only removals that leave the answer unique are kept, which is why every puzzle here can be finished by reasoning rather than guessing.
One consequence is worth knowing: on the harder settings the generator sometimes cannot reach the top of the requested blank range, because uniqueness blocks the last few removals. A puzzle asked to have 55 blanks may come back with 52. That is the guarantee working as intended, not a fault.
What the Difficulty Setting Actually Changes
| Level | Blank cells | Clues given | Typical experience |
|---|---|---|---|
| Easy | 35–40 | 41–46 | Most cells fall to scanning rows, columns and boxes for the only place a digit can go |
| Medium | 40–45 | 36–41 | Needs candidate lists and hidden singles once the easy scanning runs out |
| Hard | 45–50 | 31–36 | Long stretches with no obvious move; pairs and pointing candidates become necessary |
| Expert | 50–55 | 26–31 | Few starting footholds and deep chains of deduction from each one |
Difficulty here is set purely by how many clues remain. That is the standard approach and it correlates well with how hard a grid feels, but it is not a guarantee: clue count and solving difficulty are related rather than identical. An unusually generous arrangement of 30 clues can be easier than an awkward 34, so an occasional Expert puzzle will fall quickly and an occasional Medium will fight back. Ratings that name specific techniques require running a solver that reports which strategies it needed, which is a different job from generating the grid.
Some Numbers Behind the Grid
- 17 is the minimum. No Sudoku with 16 or fewer clues can have a unique solution; this was settled by exhaustive computer search in 2012. Puzzles at that limit are rare and very hard, well below anything this generator produces.
- There are about 6.67 × 1021 complete grids that satisfy the rules, so running out of distinct puzzles is not a practical concern.
- The digits are arbitrary symbols. No arithmetic is involved — replacing 1 to 9 with nine letters or colours gives exactly the same puzzle, which is why Sudoku is a logic exercise rather than a maths one.
- A well-formed puzzle never needs a guess. If you find yourself picking one of two possibilities at random, there is a deduction you have not spotted yet.
Frequently Asked Questions
Yes. Every puzzle generated has exactly one unique solution. The generator uses a backtracking algorithm to create a complete valid grid, then carefully removes numbers while ensuring the puzzle remains solvable with a single solution.
The setting changes how many cells are left blank: 35-40 on Easy, 40-45 on Medium, 45-50 on Hard and 50-55 on Expert. Fewer clues generally means longer chains of deduction, so harder grids tend to need candidate lists, hidden singles and pairs rather than simple scanning. Clue count is a good proxy for difficulty but not a promise — the arrangement of the clues matters too.
Yes. Enable the "Printable Format" option before generating, then click "Print" to open a clean, printer-friendly version of the puzzles. The printable format removes UI elements and optimizes layout for paper. Clear "Include Solution" first if you do not want the answers on the same sheet.
Because uniqueness always wins. Each clue is only removed if the grid still has exactly one solution afterwards; when a removal would create a second solution the number goes back. On the hardest settings that can stop the generator a few cells short of the target, so an Expert puzzle may finish with 52 blanks rather than 55.
No. The grid construction, the removal loop and the uniqueness check all run in JavaScript in your browser, so nothing is sent anywhere and no account is needed. It also means a fresh batch is genuinely random each time rather than pulled from a stored library.
No. Every puzzle is verified to have exactly one solution, which means it can be finished by logical deduction alone. If you reach a point where two digits both seem possible, the deduction that separates them is somewhere else on the grid — usually a hidden single in a box, or a pair that eliminates candidates from a row.
Up to ten per batch, and each is built from its own randomly generated complete grid, so duplicates within a batch do not occur in practice. Generate again for another ten — there is no daily limit, since the work happens on your own device.
Use Cases
Building a Week's Puzzle Sheet
Generate seven grids that step up from Easy to Expert, print them without solutions, and keep one answer sheet aside for checking.
Handing Every Student a Different Grid
A teacher runs three batches of ten Easy puzzles so nobody in the class can copy from a neighbour, and keeps the solutions for marking.
Something to Do on a Long Flight
Print a stack of Medium and Hard grids the night before travelling, so the entertainment does not depend on a battery or a signal.
Running a Timed Head-to-Head
Generate one batch at a single difficulty and give each player a different grid from it, so everyone races comparable puzzles rather than the same one.
Test Data for a Solver
A developer writing a Sudoku solver copies ten Expert grids as plain text to use as fixtures, with the bundled solutions as the expected output.