Sudoku Tips

Tips for solving a sudoku more easily with the right strategies. Start at the top with the basics, and work your way down to the techniques that crack the hardest puzzles.

1. Start with the numbers you see most

Count which number already appears most often in the grid. If there are seven 4s, the last two 4s are usually easy to place. Filling in a number completely early on gives you a clean start and often opens up the rest of the puzzle.

2. Scan rows and columns (cross-hatching)

Pick a number and a 3x3 box that is missing it. Look along the rows and columns that pass through the box. Every row and column that already contains the number rules out the squares it crosses. If only one square is left, the number goes there. Move through all nine boxes for each number from 1 to 9. This one technique solves most easy puzzles.

3. Use pencil marks

When scanning stops working, write the possible numbers (the candidates) in small print in each empty square. It takes a few minutes, but it shows patterns you can't see otherwise. In our online sudoku, turn on Notes to pencil in candidates. When you place a number, remember to remove it from the notes in the same row, column and box.

4. Look for naked singles

A naked single is a square with only one candidate left. Once your pencil marks are in place, these are easy to spot: any square with a single small number can be filled in straight away.

5. Look for hidden singles

A hidden single is a number that can only go in one square of a row, column or box, even if that square has other candidates too. For example, if 7 appears as a candidate in just one square of a box, that square must be 7. Hidden singles are easy to miss, so check each number in each box.

6. Naked pairs and triples

If two squares in the same row, column or box have exactly the same two candidates, for example 3 and 8, those two numbers must go in those two squares. You can then remove 3 and 8 from every other square in that row, column or box. The same works with three squares that share three candidates between them.

7. Pointing pairs (box and line)

If, inside a 3x3 box, a candidate only appears in one row, the number must be in that row within that box. So you can remove it from the rest of that row outside the box. The same logic works for columns, and in reverse: if a number in a row can only be placed inside one box, remove it from the other squares in that box.

8. X-Wing for hard puzzles

Find a number that can go in exactly two squares in each of two rows, where those squares line up in the same two columns. The four squares form a rectangle. The number must be in two opposite corners, so you can remove it from every other square in those two columns. X-Wing looks advanced, but once you know the shape you will start spotting it.

9. Don't guess

Every proper sudoku, including all puzzles on SudokuPuzz.com, has exactly one solution that can be found by logic. If you feel you have to guess, look again for a hidden single or a pair you have missed. Guessing usually leads to mistakes that only show up much later.

10. Check your work and take breaks

A single wrong number can ruin a whole puzzle. Use the Check button in our game to circle mistakes. And if you are stuck, step away for a few minutes. Fresh eyes often see the next move right away.

Want the step-by-step basics? Read how to solve sudoku. Totally stuck on a puzzle from a newspaper or book? Use our sudoku solver to reveal one number at a time.