How to solve Sudoku: rules and strategies for beginners

The rules

Place each digit once in every row, every column and every box outlined in bold. On a 6×6 board the digits are 1 to 6 and the boxes are 2×3; on a 9×9 board they're 1 to 9 and the boxes are 3×3.

1. Scan one digit at a time

Pick a digit, say 4, and look at a box that doesn't have it yet. Every 4 elsewhere rules out its row and column. Often only one cell in the box is left, and that's where the 4 goes.

2. Single candidates

Now pick a cell instead of a digit. List what its row, column and box already contain. If only one digit is missing from all three, it's the answer.

3. Hidden singles

Sometimes a cell has several candidates, but one of them can't go anywhere else in its row, column or box. Then it must go here, even though the cell itself looked open.

4. Pairs with notes

Turn on notes for harder boards. When two cells in the same row, column or box share the same two candidates, those two digits are spoken for: remove them from every other cell in that unit. This often unlocks the rest.

Common mistakes

• Guessing and moving on. One wrong digit can ruin the whole grid.
• Not updating notes after placing a digit.
• Only scanning rows. Boxes give the most information early on.