Sudoku rules, tips and solving techniques
Start with the rules, learn to read candidates, then practise solving techniques with worked examples and short exercises.
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Subscribe by RSS ↗Mini, classic or Killer Sudoku: where should you start?
New to Sudoku? Start with a 4×4 mini puzzle to practise rows, columns and boxes. Move to an easy 9×9 classic puzzle when you can explain each placement. Try Killer Sudoku when you want to combine those rules with sums. A smaller grid is a gentler starting point, not a guarantee that every puzzle is easy.
| Mode | Rules at a glance | First practice |
|---|---|---|
| Mini Sudoku · 4×4 | Use 1–4 once in each row, column and 2×2 box. No arithmetic is needed. | Follow a complete first puzzle |
| Classic Sudoku · 9×9 | Use 1–9 once in each row, column and 3×3 box. Digits are symbols, not a calculation. | Play an easy classic puzzle |
| Killer Sudoku · 9×9 | Keep the classic rules. Each outlined cage adds to its small total, with no repeated digit inside that cage. | Learn cages and the rule of 45 |
Mini Sudoku · 4×4
Play free 4×4 mini Sudoku online. Learn with numbers 1–4, simple 2×2 boxes, hints and new beginner puzzles.
Killer Sudoku
Classic Sudoku rules, plus one twist: each dashed cage adds up to its small number. No repeated digits inside a cage.
Take Sudoku to paper
Four 4×4 puzzles, separate answers and a first-puzzle walkthrough.
A little Sudoku in your day
Short practice, honest answers and no pressure to beat the clock.
Five minutes of Sudoku: find one good move, not a fast finish
Not sure where to look first? Try a short practice routine with one modest goal: a move you can explain.
→Everyday Sudoku · 2 minIs Sudoku good for you? Enjoy the puzzle, skip the brain-boost hype
A clear little challenge can be reason enough to play. Here is what Sudoku lets you practise—and what brain-health research does not prove.
→Your first puzzle
Understand the rules and build reliable notes.
Sudoku for beginners: one rule is enough
No arithmetic and no guessing. Once you understand rows, columns and boxes, you are ready.
→Beginner · 5 minSudoku pencil marks: how to write and update candidates
Learn Sudoku notes on a complete 9×9 puzzle: calculate candidates, update them after two proven moves, then practise the same free puzzle.
→Find the next number
Two ways to prove that a digit is certain.
When singles run out
Remove candidates, then look for singles again.
Naked pairs in Sudoku: two cells that eliminate two digits
See exactly when two matching candidate sets form a naked pair, where you can erase their digits, and when the pattern does not apply.
→Intermediate · 3 minLocked candidates: pointing pairs and box-line reduction
When a digit is confined to one line inside a box, use that overlap to remove candidates. Learn both directions with a concrete example.
→Practice · 3 minStuck on Sudoku? A step-by-step checklist before guessing
Check mistakes, repair notes and scan the simplest patterns in a useful order. Know when a hint is helping and when it is only revealing an answer.
→Questions before your first game
Do I need to guess to solve Sudoku?
Start by proving each placement from the rules. If you get stuck, check your candidate notes, then look for naked singles and hidden singles. A unique solution does not mean every step is easy; revealing an answer is different from explaining a logical move.
What to do when you are stuck →What is the difference between a naked single and a hidden single?
A naked single is a cell with only one possible digit. A hidden single is a digit with only one possible position in a row, column or box, even if that cell has other notes.
See a hidden-single example →Can I print a Sudoku and solve it on paper?
Yes. Open a classic, mini or Killer puzzle and choose Print puzzle. The print layout uses the starting clues rather than your entered answers; Killer cages and totals are included. Your browser can print it or save it as a PDF.
Choose a mini puzzle to print →Are the puzzles generated, and will refreshing give me a new one?
The games generate puzzles from a puzzle number. Classic and Killer choose a random number for a new game; mini advances to the next number. Refreshing normally restores this browser’s saved game. The daily classic puzzle is fixed for each UTC date, and the first mini lesson is a fixed teaching example.
Play classic Sudoku →