How to Play Sudoku: Rules and Your First Number

A standard Sudoku board has nine rows and nine columns, making 81 squares. Thicker lines divide it into nine smaller 3x3 boxes. Every square belongs to one row, one column, and one box at the same time. A number placed in a square must fit all three.

The filled-in numbers are clues, not numbers to rearrange. On Puzzle Game Hub they appear in the grid when a new game starts, and you cannot select one to replace it. Empty squares are the places you fill. The aim is a complete board that satisfies all three rules, not a particular score or speed.

Each row needs all the digits 1 through 9, with no repeats. The same is true for each column and each 3x3 box. These are not separate mini-games: an entry that seems to fit its row may still be blocked by its column or box.

For example, if you want to place 4 in an empty square, check the nine squares across its row, the nine down its column, and the nine in its outlined box. If any of those already contains 4, that square cannot be a 4. The same check works for every digit.

• Row: each digit appears once.
• Column: each digit appears once.
• 3x3 box: each digit appears once.

Start where most of the work is already done. Imagine a row showing 1, 2, 3, 4, 5, 6, 7, 8 and one empty square. The missing digit is 9. In a valid puzzle, that final square must be 9. You have made a deduction rather than a guess.

Most rows will have more than one gap. In that case, scan a nearly full 3x3 box or column instead. Pick one missing digit and check which empty squares are ruled out by the crossing rows and columns. You only need one certain placement to start; after entering it, another area may become easier.

Open the Sudoku game linked above and choose Easy, Medium, or Hard. Easy reveals more starting numbers, making it the friendliest place to learn the layout. Click an empty square, then choose a digit from the number pad. On a keyboard, you can type 1 through 9 into the selected square, use arrow keys to move your selection, and press Backspace or Delete to clear an editable square.

The game marks an incorrect entry and counts mistakes. The Clear button removes your entry from the selected square; it does not erase a clue. New Game starts another board. The Hint button fills one correct empty square. A hint can help you move on, but it does not explain the reasoning, so try to identify why that digit fits afterward.

The most common error is checking only a row. Every entry must also fit its column and box. Another is placing a number because it looks likely. A legal possibility is not always the correct answer; wait until the surrounding clues rule out every alternative.

Do not worry about doing math. The digits work as labels: you never need to add them to a target total. You also do not need to work from the top-left square to the bottom-right square. Move to whichever area has the clearest clue, and return to the difficult gaps later.

You are done when every empty square has been filled correctly and every row, column, and 3x3 box contains the digits 1 to 9 once. A filled grid with an incorrect entry is not a solved Sudoku. On this site, the game checks the finished board against its generated solution and displays a completion message when you have filled it correctly.

Try one Easy board at your own pace. If you understand the three rules but get stuck finding the next number, move to the companion article on solving Sudoku. It explains how to narrow down possibilities without guessing.