How to Play Sudoku

The Rules of Sudoku

A sudoku board is a 9 by 9 grid, divided into nine 3 by 3 boxes. Your goal is to fill every empty cell with a number from 1 to 9 so that:

• Every row contains 1 to 9 exactly once.
• Every column contains 1 to 9 exactly once.
• Every 3 by 3 box contains 1 to 9 exactly once.

Some numbers are already filled in at the start — these are the givens, and they never change. A well-made puzzle has exactly one solution. You never need to guess; every move can be worked out with logic.

Easy Techniques for Beginners

1. Scan rows and columns

Pick a number, say 1. Look at each row, column and box that already contains a 1 — the remaining empty box must hold the last 1. Cross out impossible cells until only one cell is left.

2. Use the "only one spot" trick

Inside any 3 by 3 box, if a number can only go in one empty cell, place it there. This single-cell placement is the most common beginner technique.

3. Pencil in candidates

In each empty cell, lightly note which numbers are still possible. Cells with just one candidate are solved for free.

Tips to Get Better

• Start easy: our Easy level is perfect for learning the rules.
• Work in pencil: write candidates in every cell before deciding.
• Use the Note mode in our sudoku game to keep candidates tidy.
• Stuck? Use the Hint button to reveal the next correct number.
• Move up to Medium, Hard and Expert as you improve.

Ready? Play sudoku online free right now — no download, and your progress is saved as you go.