How to play Sudoku: rules and beginner techniques

Updated 2026-10-30

To play Sudoku, fill a 9×9 grid so that every row, every column and every 3×3 box contains each digit from 1 to 9 exactly once. You never need to guess: a well-made puzzle has exactly one solution, and you can reach it with logic alone.

The rules of Sudoku

A standard Sudoku grid has 81 cells, arranged in nine rows, nine columns and nine 3×3 boxes (sometimes called blocks or regions). Some cells already contain digits when you start. These are the givens, and you cannot change them. Your job is to fill every empty cell so that:

• each row contains the digits 1–9 once each,
• each column contains the digits 1–9 once each,
• each 3×3 box contains the digits 1–9 once each.

That is the whole rule set. There is no arithmetic involved; the digits are just nine different symbols, and you could play the same puzzle with letters or colours. What makes Sudoku interesting is how those three overlapping constraints interact.

Why a good Sudoku has a unique solution

A properly constructed Sudoku has exactly one valid way to fill the grid. This matters for solving: it means every placement can be justified by reasoning, and if you ever feel you must guess, there is a deduction you have not spotted yet. The number of givens does not decide difficulty on its own. A puzzle with few givens can be easy, and one with many can be hard; what counts is which techniques you need to make progress.

Beginner Sudoku techniques

Scanning

Scanning is where almost everyone starts. Pick a digit, say 5, and look at where the 5s already are. Each placed 5 rules out its row, its column and its box. If, inside one box, only a single cell is left where a 5 could go, write it in. Sweep through the digits 1 to 9 and through every box, and you will often fill a good part of an easy puzzle this way.

Hidden singles

Scanning is really a hunt for hidden singles: a digit that has only one possible home within a row, column or box. The cell itself may still look as if it could hold several digits, which is why the single is "hidden". Checking rows and columns as well as boxes finds many more of them.

Naked singles

A naked single is the opposite view. Look at one empty cell and list every digit already present in its row, column and box. If eight different digits are ruled out, the remaining one must go in that cell. Naked singles are common in the middle of a solve, once the grid has filled up a little.

Pencil marks and candidates

When singles run dry, start writing candidates: small pencil marks in each empty cell showing which digits are still possible there. It takes a few minutes, but it turns hidden information into something you can see. Every time you place a digit, erase it from the candidates of the cells it can see. Many apps let you toggle a notes mode for exactly this.

Naked pairs

Suppose two cells in the same row each have only the candidates 3 and 7. You do not yet know which is which, but between them they must use up the 3 and the 7. So no other cell in that row can be a 3 or a 7, and you can erase those candidates elsewhere in the row. The same idea works in columns and boxes, and it extends to triples: three cells whose candidates are drawn only from the same three digits.

Hidden pairs

A hidden pair is when two digits can appear in only the same two cells of a unit. If, in a box, the digits 2 and 8 are possible only in cells A and B, then A and B must be 2 and 8, and any other candidates in those two cells can be removed.

Pointing (box–line interaction)

If every possible spot for a digit within a box lies in a single row, that digit must sit in that row inside the box. That means it cannot appear anywhere else in the same row outside the box. This simple interaction unlocks many medium puzzles.

Sudoku and Latin squares

A finished Sudoku is a special kind of Latin square: an n×n grid filled with n symbols so that each symbol appears once in every row and every column. Latin squares have been studied by mathematicians for centuries. Sudoku adds one extra condition, the 3×3 boxes, and turns the object into a puzzle by removing most of the symbols and asking you to restore them.

A short history

The modern puzzle first appeared in American puzzle magazines under the name Number Place. It was later taken up in Japan, where the publisher Nikoli gave it the name Sudoku and helped popularise it, before it spread worldwide in newspapers and on phones.

Where to go next

Once the basics feel comfortable, try a variant. Killer Sudoku adds cage sums to the grid, and Kakuro drops the givens entirely in favour of arithmetic clues. For a broader tour, see our list of puzzles like Sudoku.

If you enjoy the "each row, column and region exactly once" feeling, you will probably like Star Battle too. Instead of digits you place stars, and stars may not touch, which brings a whole new set of deductions. Read how Star Battle compares with Sudoku, or simply play Star Battle for free right now.