The goal
Fill every empty cell with a number from 1 to 9 so that no number repeats in any row, column or 3×3 box. Some cells already hold numbers. Those are the clues, and they cannot be changed.
The grid
The grid is 9×9, which makes 81 cells. It is divided into nine rows, nine columns and nine 3×3 boxes. Every cell belongs to exactly one row, one column and one box, and each of those 27 groups must end up holding 1 to 9 once.
The one rule
A number may appear only once in its row, once in its column and once in its 3×3 box.
Example: if a row already holds a 5, no other cell in that row can be a 5. If the box a cell sits in also holds a 5, that cell is ruled out for a 5 as well.
Clues and difficulty
Pick Easy, Medium or Hard. They start with 44, 36 and 28 given numbers. Every puzzle has exactly one solution, so you never need to hunt for a second answer (how many starting numbers a puzzle has, does every Sudoku have one solution).
Entering numbers
Select an empty cell, then use the number pad or your keyboard to enter a number. The arrow keys move between cells. Use Erase to clear a cell you filled in. If a number repeats in its row, column or box, the game highlights it as a conflict.
The game only checks for repeats. It does not say whether a number is the right answer (do you have to guess).
Pencil notes and undo
Turn on Notes (or press N) to mark which numbers an empty cell could still be. When you place a number, the game clears it from the notes of every cell in the same row, column and box (what pencil notes do).
Undo steps back through up to 100 changes, notes included (how many moves you can undo).
Winning
You win when every cell is filled and nothing repeats in any row, column or box. Because each puzzle has one solution, a full grid with no conflicts is the answer (when is a Sudoku solved).
Putting the rules to work
New to solving? Start on Easy and scan for numbers that fit in only one place. The Sudoku solving techniques guide goes from single numbers to pairs and pointing, or play Sudoku free with saved progress and no sign-up.
Sudoku rules questions
How many starting numbers does a Sudoku puzzle have?
Easy starts with 44 given numbers, Medium with 36 and Hard with 28. Every puzzle still has exactly one solution, whichever level you choose.
Read the full answer →Does every Sudoku puzzle have only one solution?
Yes. Each puzzle is checked so that exactly one way of filling the grid satisfies every row, column and box, so there is one right answer.
Read the full answer →Do you have to guess in Sudoku?
No. Every puzzle has one solution, so a wrong number always ends in a contradiction. Use notes to narrow cells down before you commit to a number.
Read the full answer →What do pencil notes do in Sudoku?
Notes mark every number a cell could still be. When you place a number, it is cleared from the notes of every cell in its row, column and box.
Read the full answer →How many moves can you undo in Sudoku?
Up to 100. Undo steps back through your numbers and notes one change at a time, and it works only within the puzzle you are playing.
Read the full answer →When is a Sudoku puzzle solved?
When every cell is filled and no number repeats in any row, column or 3×3 box. Repeats are highlighted as conflicts while you play.
Read the full answer →Do you need to be good at math to play Sudoku?
No. Sudoku uses the digits 1 to 9 only as labels. There is no adding or counting, just checking which numbers are missing from a row, column or box.
Read the full answer →Play Sudoku free →Your game is saved in this browser. No sign-up.