How to Play Sudoku

To play Sudoku, fill every empty cell of a 9x9 grid with a digit from 1 to 9 so that no digit repeats in any row, column or 3x3 box. Some cells are filled in at the start, and you use them to work out the rest by logic. You never need to guess and you never need to add anything up. This guide is for complete beginners and takes you from the rules to your first placement.

Sudoku rules

A finished grid obeys three rules at once:

• Row rule: each of the 9 rows holds the digits 1 to 9 exactly once.
• Column rule: each of the 9 columns holds the digits 1 to 9 exactly once.
• Box rule: each of the nine 3x3 boxes holds the digits 1 to 9 exactly once.

Rows, columns and boxes are all called units. Every cell belongs to exactly one row, one column and one box, and a digit you place must fit all three. Since a unit has nine cells and needs nine different digits, every digit appears exactly once in each unit.

The grid: rows, columns, boxes and candidates

The grid has 81 cells. Rows run across and columns run down. This page names a cell by row letter then column number. Rows are A to J from the top (the letter I is skipped) and columns are 1 to 9 from the left, so A9 is the top row, right-hand column. The thick lines mark the nine boxes, numbered left to right, top to bottom.

• Givens (also called clues) are the digits printed at the start. They never change.
• Candidates are the digits that could still go in an empty cell. A digit is a candidate only if its row, column and box do not already contain it.
• Pencil marks (notes) are candidates you write in small print inside a cell so you do not have to work them out again.

The board below shades one of each unit on an Easy puzzle: row D (across), column 7 (down) and box 1 (top left). Large digits are givens, small digits are candidates.

Your first placement: a worked example

Here is the top row of the same Easy puzzle, from our own catalogue. Row A already holds 3, 6, 5, 2, 4 and 9, so the digits missing from it are 1, 7 and 8. Take the empty cell at the right end, A9, and test each missing digit:

1. 1 is out: column 9 already has a 1 (in C9).
2. 7 is out: column 9 also has a 7 (in J9), and box 3 has one in B8.
3. 8 is left: nothing in row A, column 9 or the top-right box contains an 8.

Only 8 fits, so A9 is 8. This is called a naked single: a cell with exactly one candidate. Easy puzzles are mostly solved by repeating this check, and by its mirror image, the hidden single, where a digit has only one possible cell left inside a unit. Both are covered step by step in how to solve Sudoku.

Sudoku for beginners: how to start

1. Scan for the digits that appear most often in the givens. A digit with many copies on the grid leaves few places for its remaining copies.
2. Look at rows, columns and boxes that are nearly full. Fewer empty cells means fewer candidates.
3. For each empty cell, remove the digits its row, column and box already contain. If one remains, place it.
4. Place, then repeat: every new digit removes candidates from about twenty other cells.
5. When no cell is obviously forced, switch to pencil marks and look for a digit that fits only one cell of a unit.

Start on the Easy level. Our levels run Easy, Medium, Hard, Expert, Master and Legendary, and they are graded by the hardest solving step a puzzle needs, not by how many digits are given.

Playing on Sudoku69

Tap a cell, then tap a digit on the number pad to place it. Below the board are three buttons: Undo, Erase and Note Mode. Note Mode shows an ON or OFF badge. While it is ON, the number pad adds or removes pencil marks in the selected cell instead of placing a digit. Turn it OFF to place digits again. Undo steps back through your moves, so a wrong turn costs nothing.

Is Sudoku maths?

Not in the sense of arithmetic. The digits could be nine letters or nine colours and the puzzle would work the same, because nothing is added, subtracted or multiplied. Solving is pure logic and elimination, although the structure behind the grids is a real topic in mathematics. See Sudoku maths for how many grids exist and why clue counts matter.

Does every Sudoku have one solution?

A well-made puzzle does, and that is what makes it fair. If a puzzle had two solutions, no logical step could ever choose between them, so you would be forced to guess. On Sudoku69, any puzzle our solver cannot finish by logic alone is never published, so no puzzle here needs a guess.

Next steps

Once the rules feel natural, learn the solving methods in the step by step guide. The same idea also comes in other shapes: Killer Sudoku replaces most givens with sum cages, and 16x16 Sudoku uses larger 4x4 boxes.