Sudoku Generator
Sudoku generator for 4×4, 6×6 and 9×9 with four difficulty levels — play directly online with pencil marks, hints, error check and undo, or download/print as PDF for offline play.
Every generated puzzle is unique with exactly one valid solution. The 4×4 variant suits children and beginners learning to play sudoku, 6×6 adds an extra challenge, and 9×9 is the classic sudoku for advanced solvers. Play sudoku online with auto pencil marks, error checking, hints, a built-in timer and auto-save — or print as PDF to play offline.
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How does sudoku work?
Sudoku is a logic puzzle with a grid divided into blocks. The goal is to fill every empty cell with a digit. Our generator creates online sudoku to play directly in your browser in three sizes: 4×4 (with 2×2 blocks), 6×6 (with 2×3 blocks) and 9×9 (with 3×3 blocks) — or download as PDF to print.
The rules
- Each digit may appear only once in each row.
- Each digit may appear only once in each column.
- Each digit may appear only once in each block.
How to solve it
- Start with cells where only one digit fits — see which digits are already in the row, column or block.
- Work one digit at a time: see where it can go in a block and find the only place it fits.
- When unsure, write candidates as small notes in the cell using note mode.
- Stuck? Click the hint button for a helping hand.
How to make a sudoku with the online generator
- Pick the size of your sudoku. Choose between 4×4 (easy), 6×6 (extra challenge) or 9×9 (classic). The 4×4 variant is ideal for children and beginners, 9×9 is the standard size found in newspapers.
- Pick a difficulty level. Easy, Medium, Hard or Expert. Every level produces a unique puzzle with exactly one valid solution — no guessing required.
- Click "Generate puzzle". The generator instantly creates a new sudoku. Not happy with the puzzle? Click again for a different one — you can generate unlimited puzzles.
- Play online or print the puzzle. Solve the sudoku directly in your browser, or download as PDF (1 or 4 puzzles per page) or JPG to print and solve on paper.
- Use notes and hints when stuck. Write candidate digits as small notes in a cell using note mode. Stuck? Click the hint button for a tip with explanation of the technique (Naked Single, Hidden Single, and so on).
- Check your work. Click "Check" to see whether you have made mistakes so far. Switch on "Highlight duplicates" for live feedback while playing.
Frequently asked questions
What is sudoku?
Sudoku is a logic-based number puzzle solved by filling digits into a grid. Every row, every column and every block must contain all the digits without repetition. The classic version is 9×9 with digits 1-9, but smaller variants like 4×4 and 6×6 also exist. Sudoku is not a math puzzle — you don't need to count or add, only reason logically.
What age can you start playing sudoku?
Sudoku is suitable from about 5 or 6 years old, once a child recognises numbers and can count up to the maximum of the grid size. For young children (5-7), 4×4 with digits 1-4 works best. From 7-8 years on, children can handle 6×6, and from 9-10 the classic 9×9. There is no upper age limit — many adults and seniors play sudoku daily for relaxation or brain training.
Is sudoku good for your brain?
Yes, playing sudoku regularly exercises several cognitive skills at once: logical reasoning, pattern recognition, short-term memory and concentration. Research suggests puzzles like sudoku are associated with maintaining cognitive function in older adults, though the direct link to dementia prevention is still being studied. For children, sudoku strengthens number recognition and perseverance. It is also a calm, low-screen activity — even online, you play slowly and deliberately.
What is the difference between 4×4, 6×6 and 9×9 sudoku?
The numbers indicate the grid size. 4×4 sudoku has 16 cells divided into 2×2 blocks and uses digits 1-4 — ideal for children and beginners. 6×6 sudoku has 36 cells in 2×3 blocks with digits 1-6 — a good middle step. 9×9 sudoku has 81 cells in 3×3 blocks with digits 1-9 — this is the classic variant found in newspapers and puzzle books. The rules are the same for all three: each digit may appear only once per row, column and block.
Does every generated sudoku have exactly one solution?
Yes, every sudoku this generator creates has exactly one valid solution — a core requirement of a real sudoku. The algorithm first builds a fully solved grid and then removes digits one by one while checking that the puzzle remains uniquely solvable. This guarantees you never have to guess: pure logic always leads to the solution.
What techniques are used to solve sudoku?
The basic techniques are Naked Single (only one digit fits in a cell) and Hidden Single (a digit can only go in one place within a row, column or block). More advanced solvers use Naked Pair, Hidden Pair, Pointing Pair and X-Wing. Our hint button names the technique that applies to your puzzle, with a short explanation of why. For deeper explanations of each technique, see the sudoku solver — it shows step by step how a puzzle is fully solved.
How long does it take to solve a sudoku?
It depends on grid size and difficulty. A 4×4 easy typically takes 1-2 minutes. A 9×9 easy takes a beginner 10-20 minutes and an experienced player 3-5 minutes. 9×9 hard can take 15-30 minutes, expert level 30-60 minutes or more. World records for 9×9 are under 1 minute, but those are exceptional. Our built-in timer shows your time so you can track your progress.
Can I play sudoku directly online without installing anything?
Yes — all features work directly in your browser on desktop, tablet or phone. You do not need to install an app, create an account or register. Click Generate puzzle and you can start straight away. Your progress is automatically saved locally in your browser, so you can come back later and continue where you left off — see the question about game saving below.
Is the sudoku generator free?
Yes, the generator is completely free and you do not need an account. You can generate unlimited sudokus in all three sizes and all four difficulty levels, and print or download as many as you want.
Can I print or download sudokus as PDF?
Yes — use the PDF (1) button for one puzzle per A4 page, or PDF (4) for four puzzles per page (handy for schools and libraries). With JPG you download an image. To print directly, open the PDF and print from your browser or PDF viewer.
Does the sudoku generator work on tablet or phone?
Yes, the generator works on desktop, tablet and phone. On touch screens you tap a cell and then the digit in the numpad. Notes, hints, undo/redo and pause all work the same as on desktop. On smaller screens you can use the phone in portrait or landscape — the layout adapts.
Is my game saved while playing?
Yes, your current game is automatically saved in your browser. If you close the page and come back later, you continue where you left off — including your notes, filled-in digits, time and hint count. The save is per device and browser (local storage), not tied to an account. On a different browser or device you will not see the game.