The goal of Sudoku
A Sudoku puzzle starts with some numbers already placed. Your job is to fill every empty cell using logic. A completed puzzle must satisfy all three rules at the same time.
Rule 1
Each row must contain the numbers 1-9 exactly once.
Rule 2
Each column must contain the numbers 1-9 exactly once.
Rule 3
Each 3x3 box must contain the numbers 1-9 exactly once.
Row, column, and box rule diagram
The diagram below shows the three rule areas you must check before placing a number: one row, one column, and one 3x3 box. A number is legal only when it does not repeat in any of those areas.
Row rule: every row contains 1-9 once.
Column rule: every column contains 1-9 once.
Box rule: every 3x3 box contains 1-9 once.
Rules of Sudoku game
The rules of Sudoku do not require arithmetic. The numbers are symbols used to track logic. A legal move must pass three checks: row, column, and 3x3 box. If one of those checks fails, the move breaks the Sudoku puzzle rules.
Can numbers repeat in Sudoku?
Yes, the same number appears many times across the whole puzzle. The important limit is local: a number cannot repeat inside the same row, same column, or same 3x3 box.
What makes a Sudoku puzzle valid?
A valid standard Sudoku puzzle should have one logical solution. If a puzzle has no solution or several solutions, it is not a good standard Sudoku puzzle.
Are 4x4 and 9x9 Sudoku rules different?
The idea is the same, but the grid size changes. A 4x4 Sudoku uses numbers 1 to 4 and smaller boxes, which makes it useful for learning. Standard Sudoku is usually 9x9 and uses numbers 1 to 9.
Rule check example
If a row already contains 8, no other cell in that row can be 8. You must check the column and box before placing the final number.
Sudoku rules for beginners
For beginners, the easiest way to remember the basic rules of Sudoku is to ask three questions before every move: is this number already in the row, is it already in the column, and is it already in the box? If the answer is no to all three, the move may be legal.
FAQ about Sudoku rules
What are the rules of Sudoku?
Each row, column, and 3x3 box must contain 1 to 9 exactly once.
What are the Sudoku game rules?
The Sudoku game rules are the same as the standard puzzle rules: no repeated number in any row, column, or 3x3 box.
What are the basic rules of Sudoku for beginners?
Beginners only need to remember the row rule, column rule, and box rule. All solving techniques build on those three constraints.
Can Sudoku have more than one answer?
A well-made standard Sudoku puzzle should have exactly one solution. If a puzzle has more than one answer, it is usually considered invalid or poorly designed.
What happens if a number repeats?
If a number repeats in the same row, column, or 3x3 box, that placement breaks the rules. You should remove it and check the affected row, column, and box again.
Practice the rules with an easy puzzle
The fastest way to remember the rules is to apply them. Start with easy puzzles and focus on checking rows, columns, and boxes before every move.