How to Play Sudoku

Learn how to play sudoku in plain English: the three simple rules, the parts of the grid, how to find your first move and what changes in killer, jigsaw and the other variants.

Sudoku is a logic puzzle. You fill a 9×9 grid with the digits 1 to 9 so that each row, each column and each 3×3 box contains every digit exactly once. The puzzle starts partly filled in; your job is to work out the rest using nothing but reasoning. There is no arithmetic and, in a properly made puzzle, no guessing.

This page is the short, friendly version of how the game works — written for someone who has never solved one before. If you are completely new, read it top to bottom. If you already know the basics and want a specific variant, jump to the variant picker further down.

The one rule that runs the whole game

Everything in sudoku comes from a single constraint. Take any group of nine cells that the puzzle treats as a unit — a row, a column or a 3×3 box — and that group has to contain every digit from 1 to 9, with no repeats. That is it. The "boxes" are the heavy-outlined 3×3 blocks; together they tile the grid into nine of them.

Because each cell belongs to one row, one column and one box at the same time, placing a digit somewhere immediately rules it out of 20 other cells. That overlap is the engine of every deduction. You never have to "try a number" — once you find a cell where only one digit is still legal, that digit is forced.

  • Each row contains 1–9 with no repeats.
  • Each column contains 1–9 with no repeats.
  • Each 3×3 box contains 1–9 with no repeats.
  • The given (pre-filled) digits never change.
The three units the rule talks about — a row, a column and a 3×3 box. Each must contain 1–9 exactly once.

The parts of the grid you need to name

A 9×9 board has 81 cells. Nine of them sit in each row, nine in each column, and nine in each 3×3 box. Rows, columns and boxes are collectively called "units" — the groups the rule applies to. The cells that share a unit with a given cell are its "peers"; there are 20 of them on a 9×9 grid.

The digits printed at the start are the "givens" or "clues". They are fixed and correct. A "candidate" is a digit that could still legally go in an empty cell — one that does not already appear in that cell's row, column or box. Solving is the steady process of narrowing each cell's candidates down to one.

Watch a cell's candidates fall: every digit already in its row, column or box rules itself out, until one remains.

How to find your first move

The fastest way into a puzzle is to scan for "singles". There are two kinds, and between them they solve most easy and medium grids.

A naked single is an empty cell where only one digit is still legal — the other eight already appear somewhere in the same row, column or box. A hidden single is a digit that has only one cell left in a particular row, column or box where it can still go. Both produce a forced placement; place it, then re-scan.

  • Pick a digit, say 1. Find every place it already sits.
  • For each box that does not yet contain a 1, see which empty cells in that box still avoid every existing 1 in their row and column.
  • If exactly one cell qualifies, that cell is a hidden single — place it and move on to the next digit.
  • For an empty cell that catches your eye, list the digits not yet used in its row, column and box. If exactly one is left, it is a naked single.
A naked single, up close: the cell sees 1, 2, 4 in its row, 3, 5, 8 in its column and 6, 9 in its box — only 7 is left.

How a real sudoku is different from a random grid of numbers

A "proper" sudoku has exactly one completion. That guarantee is what makes the puzzle solvable by pure logic, because at every step the correct move is forced rather than chosen. Publishers run new puzzles through a solver before printing them to confirm the solution is unique.

A grid with two valid completions is not really a sudoku. Solving it would, at some point, require a choice with no logical reason to prefer one branch — a guess. So if a puzzle ever seems to need a guess, either you have missed a deduction or the puzzle is broken; on a published or generated puzzle, it is almost always the first.

  • A proper sudoku has exactly one solution.
  • Two solutions ⇒ a forced guess ⇒ not a real sudoku.
  • Reputable puzzles are solver-verified to be unique before publishing.

When you should reach for a technique

Once naked and hidden singles dry up — usually on harder puzzles — you switch to elimination techniques. The two most useful first ones are the naked single you have already met (now applied to cells you only spot once candidates are tracked) and the hidden single across a unit. From there the ladder runs: locked candidates, naked and hidden pairs, fish like the X-Wing, wings like the XY-Wing, and finally chains. You only reach for harder tools when the simpler ones genuinely fail to move the grid.

You do not have to learn them all at once. Most players spend a long time on singles, then add naked pairs and pointing pairs, and only graduate to fish and wings when they want to clear expert puzzles. A short, focused list of next steps is in the techniques section.

A hidden single — the move techniques systematise: each placed 5 blocks part of Box 5, until only one cell can take a 5.

The variants, in one sentence each

Most variants keep the row, column and box rule and add or swap one constraint. Pick the variant card below for its full rules, but here is the one-line summary so you know what is on offer.

  • Classic — the original: rows, columns and 3×3 boxes contain 1–9 once each.
  • Killer sudoku — same rules plus dotted cages with little sums; the digits inside each cage must add to the printed total with no repeats inside the cage.
  • Jigsaw sudoku — the 3×3 boxes are replaced by nine irregular regions; the row, column and region rule still applies.
  • Sudoku X — classic rules plus a diagonal constraint: each of the two main diagonals must also contain 1–9 once.
  • Wordoku — classic sudoku with letters instead of digits, often spelling a word along a row or diagonal.
  • 6×6 mini sudoku — a friendlier grid using the digits 1–6 inside 2×3 boxes.
  • 4×4 kids sudoku — the smallest grid, digits 1–4 inside 2×2 boxes; designed for first-time players.

Try it yourself

1
6
9
7
2
1
8
3
3
9
2
2
5
9
7
4
3
9
1
7
8
2
6
5
5
8
1
5
9
8
7
4
6
2
3
3
4
2
8
1

Tap a cell, then a number, to practise.

Pick a variant for the full rules

Each card opens that variant's rules page with a worked example and, where the board can show it faithfully, a practice grid.

How to Play Classic Sudoku

The complete rules of standard 9×9 Sudoku, explained for absolute beginners.

Killer Sudoku Rules: 45-Rule, Cages & Strategy

Killer Sudoku rules explained: how cages and their printed sums work, the 45-rule that cracks any region, the cage-sum combinations, and a worked example.

Jigsaw Sudoku Rules

Sudoku where the nine regions are irregular jigsaw shapes instead of 3×3 boxes.

Sudoku X Rules

Classic Sudoku with two extra diagonal constraints forming an X across the grid.

Wordoku Rules

Sudoku played with nine letters instead of digits — sometimes spelling a hidden word.

Mini Sudoku (6×6) Rules

A smaller 6×6 Sudoku with 2×3 boxes — a gentle step up from 4×4.

Sudoku for Kids (4×4) Rules

The simplest Sudoku: a 4×4 grid with digits 1–4, perfect for children learning the game.

Frequently asked questions

Do I need maths to play sudoku?
No. Sudoku uses digits as labels, not quantities — you never add, subtract or count. Every move is a logical deduction about where a symbol can legally go. You could swap the digits 1–9 for nine colours or letters and the puzzle would play exactly the same. Wordoku, the letter variant, is the proof.
Is guessing ever required?
Not in a properly made sudoku. Because the puzzle has exactly one solution, every step can be reached by logic — though hard puzzles need advanced techniques to find it. If a position seems to demand a guess, almost always there is a deduction you have not spotted yet rather than a true choice.
What is the difference between classic, killer, jigsaw, sudoku X and wordoku?
Classic sudoku uses the row, column and 3×3-box rule. Killer adds dotted cages whose digits sum to a printed total with no repeats inside the cage. Jigsaw replaces the 3×3 boxes with nine irregular regions. Sudoku X adds a constraint on both main diagonals. Wordoku replaces the digits 1–9 with nine letters — the logic is identical to classic. The variant cards below give the full rules for each.
What size of grid does sudoku come in?
The classic grid is 9×9 with 3×3 boxes and the digits 1–9. Smaller versions are common for beginners: a 6×6 "mini" grid uses 2×3 boxes and the digits 1–6, and a 4×4 "kids" grid uses 2×2 boxes and the digits 1–4. The rule that every row, column and box contains each symbol once applies on all of them.
How long does a sudoku take to solve?
It depends on the difficulty and how much you have practised. An average solver finishes an easy 9×9 grid in around 5 to 15 minutes; medium puzzles tend to land between 15 and 30 minutes; hard ones run 30 to 60 minutes; expert grids can take an hour or more. Beginners are typically a few times slower until the scanning becomes automatic — and that goes quickly.
Can a sudoku have more than one solution?
A properly made one cannot. If a grid has multiple completions it is not a valid sudoku, because solving it would require an arbitrary guess. Published and generated puzzles are run through a solver to confirm a single, logically reachable answer before they ship.
What should I learn after the rules?
The two single-step techniques: naked single and hidden single. Between them they solve almost all easy and medium puzzles, and they are the foundation every harder technique builds on. The techniques section starts there and ladders up to locked candidates, pairs, X-Wings and beyond.

What to learn next

Further reading

Practice online

Put it into practice on free puzzles with hints, notes and four difficulty levels.

Play Sudoku

We use Google Analytics to understand how people use the site. No tracking cookies are set unless you accept. Read our analytics cookie policy.