How to Play Sudoku

The rule

A sudoku grid has 81 squares in nine rows, nine columns and nine 3×3 boxes. Fill every empty square with a digit from 1 to 9 so that each row, each column and each box contains every digit exactly once. That is all. There is no arithmetic: the digits could just as well be letters or colours.

A proper puzzle has exactly one solution, and you can reach it by logic alone. Every puzzle on this site is checked for that before you see it.

Finding your first digits

Look from the square

Pick an empty square. List the digits already in its row, its column and its box. If eight different digits are there, the ninth is the answer. This is called a naked single.

Look from the digit

Pick a digit, say 7, and a box that has no 7 yet. Every 7 elsewhere in the grid blocks its whole row and column. If those blocks leave only one free square in the box, the 7 goes there. This is called a hidden single, and it finds more digits than the first method.

Using notes

On harder puzzles you will run out of obvious moves. Then write small candidates in the squares: every digit that is not yet ruled out. In our game, press Notes (or N on a keyboard) and tap digits to pencil them in. As you place digits, the game clears that digit from the notes of the squares it can see.

With notes in place, look for squares down to one candidate, and for digits with only one possible square in a row, column or box.

When you get stuck

1. Recheck your last few entries: a wrong digit makes everything after it stall. Our "Show mistakes" option marks wrong digits in red if you want it.
2. Go through the digits 1 to 9 once more, looking at each box.
3. Fill in notes for the squares with the fewest options.
4. Learn one new technique from our techniques guide; each one unlocks a level.
5. Take a hint. It places one correct digit, which is often all you need to get moving.

Where to start

Begin with easy sudoku, which needs only the first method above. Move up to medium when you can finish easy puzzles without hints.