The basics
How to play Sudoku
Sudoku has one rule and no math. If you can spot where a digit can and cannot go, you can play.
Sudoku is played on a 9 by 9 grid made of nine 3 by 3 boxes. Fill the empty cells so that every row, every column and every box contains the digits 1 to 9 exactly once. Some digits are given, and logic tells you the rest.
The grid
A Sudoku grid has 81 cells. It is divided into nine rows, nine columns and nine 3 by 3 boxes. Some cells already contain a digit (these are the clues, or givens). Your job is to fill every other cell.
The one rule
Each row, each column and each 3 by 3 box must contain every digit from 1 to 9, once. That means no digit may repeat inside any of those three groups. These groups are called units. The full list of rules, with examples of what breaks them, is in the Sudoku rules.
Your first move, step by step
- Choose a digit that appears many times in the grid, such as 7.
- Cross out every row, column and box that already contains a 7. A 7 cannot go there again.
- Look at a box where only one open cell is left that is not crossed out. The 7 must go there.
- Write it in. Now choose the next digit and repeat.
That method is called a hidden single. A second one is the naked single: a cell where every digit but one is already used in its row, column or box.
Helpful habits
- Never guess. Every proper Sudoku can be solved by logic alone.
- Work with a pencil or use notes, so you can write candidate digits and remove them as you learn more. See notes and pencil marks.
- Look at what is most filled first: rows, columns and boxes with the most digits give the fastest progress.
- Take breaks. A fresh look finds a move that tired eyes miss.
Where to go next
Play an Easy puzzle, which only needs the two ideas above. Then read the beginner guide for a plan to improve.
Frequently asked questions
What is the aim of Sudoku?
To fill the whole 9 by 9 grid so every row, column and 3 by 3 box has the digits 1 to 9 once each.
Do I need to be good at math?
No. The digits could be letters or colors. Sudoku is about logic.
Where should I start in a Sudoku?
Start with the row, column or box that has the most digits, or choose a digit that appears often and find where it fits.
Can I guess in Sudoku?
You should not. A good puzzle can always be solved with logic, and guessing tends to lead to a contradiction later.