Sudoku rules
Sudoku rules explained
The objective, legal moves, and the few facts that hold on every standard Sudoku board.
A classic Sudoku is a 9x9 grid split into nine 3x3 boxes. Fill every empty square so each row, column, and box contains the digits 1 through 9 exactly once.
The only rules you need
- Fill the grid with the digits 1 to 9.
- No row can repeat a digit.
- No column can repeat a digit.
- No 3x3 box can repeat a digit.
What the given clues mean
The numbers printed at the start of the puzzle are fixed clues. They are the starting structure of the board, so they cannot be erased or changed.
Those clues define the logic space you work inside and give every later placement its meaning.
How to tell whether a move is legal
If you place a digit in one square, that same digit cannot already appear in the square's row, column, or 3x3 box.
When more than one candidate still seems possible, do not force a move. Leave the square open or use notes until the board gives clearer information.
Quick questions
Do I have to fill the blanks in order?
No. You can solve any part of the grid first. Most players jump to the row, column, or box that already looks closest to completion.
Should a proper Sudoku have one solution?
Yes. A well-made Sudoku puzzle is built around one valid finish, even if the logic needed to reach it becomes harder.