Sudoku Puzzle
Play free Sudoku online. Choose easy, medium, or hard difficulty. Use the hint button if you get stuck, or check your solution at any time.
How to Play Sudoku
How to play Sudoku: fill every empty cell in the 9×9 grid with a number from 1 to 9. Each row, each column, and each of the nine 3×3 boxes must contain every number from 1 to 9 exactly once. The starting numbers (given clues) cannot be changed.
Start by scanning rows, columns, and boxes to find cells where only one number is possible. These single possibility cells are the easiest starting points. As you fill in numbers, new single possibilities will open up. For harder puzzles, use pencil mark notation to track which numbers are still possible in each cell.
Sudoku Solving Strategies
The most important beginner strategy is called Singles. A naked single is a cell where only one number is possible. A hidden single is a number that can only go in one cell within a row, column, or box, even if that cell appears to have multiple candidates.
For medium difficulty, learn to spot pairs. A naked pair is two cells in the same row, column, or box that can only contain the same two numbers. This eliminates those two numbers from every other cell in that unit.
Frequently Asked Questions
To play Sudoku, fill in the 9×9 grid so that every row, every column, and every 3×3 box contains the digits 1 through 9 with no repeats. Cells that are already filled in are given clues. Use logic to determine which number belongs in each empty cell.
The rules of Sudoku are: each row must contain the numbers 1 to 9 with no repetition, each column must contain the numbers 1 to 9 with no repetition, and each of the nine 3×3 boxes must contain the numbers 1 to 9 with no repetition. Every valid Sudoku puzzle has exactly one solution.
The best strategy for beginners is to find cells that can only contain one possible number. Scan each row, column, and box for missing numbers and eliminate possibilities. Look for the number that appears most often and place it first. For harder puzzles, use pencil marks to track candidates in each cell.
The hardest Sudoku difficulty level is called expert or diabolical. These puzzles require advanced techniques such as X-Wing, Swordfish, and Forcing Chains. Hard puzzles typically have fewer than 25 given clues, requiring more complex logical deduction to solve.
An easy Sudoku puzzle can be solved in 5 to 10 minutes by a beginner. A medium puzzle typically takes 10 to 20 minutes. A hard or expert puzzle may take 30 minutes to an hour or more, depending on experience. With practice, solving times improve significantly.