Sudoku tips and techniques
Quick answer: scan each digit 1–9 across the boxes, fill any cell with a single candidate, and look for digits with only one home in a row, column or box. For hard puzzles, add pencil marks and use pointing pairs and naked pairs to remove candidates.
Techniques by difficulty
| Technique | Needed for |
|---|---|
| Scanning (cross-hatching) | Easy |
| Naked single | Easy |
| Hidden single | Easy / Medium |
| Pointing pair / triple | Hard |
| Box/line reduction | Hard |
| Naked pair | Hard |
| Hidden pair, X-Wing | Expert |
1. Scanning (cross-hatching)
Choose a digit and trace the rows and columns where it already appears. In each box, the remaining open cells for that digit shrink fast. When only one is left, place it. Go through 1 to 9 in order so you don't miss anything.
2. Naked single
Look at a cell and rule out every digit already in its row, column and box. If only one digit is left, that's the answer for the cell.
3. Hidden single
Look at a row, column or box and ask: where can the 4 go? If only one cell can take it, the 4 goes there, even if that cell had other candidates too. This is the most useful technique in all of Sudoku.
4. Pointing pairs and triples
If every candidate for 6 inside a box sits in the same row, the box's 6 is somewhere in that row. So no other cell of that row (outside the box) can be 6. Cross those candidates off.
5. Box/line reduction
The mirror image: if a row's only candidates for 2 are inside one box, the 2 for that box must be in that row, so remove 2 from the box's other rows.
6. Naked pairs
Two cells in a unit with the same two candidates, like {3,8} and {3,8}, lock those digits. Remove 3 and 8 from every other cell in that row, column or box. The same idea extends to triples.
7. Hidden pairs
If two digits can only go in the same two cells of a unit, those cells hold those digits. Every other candidate in those two cells can be removed.
8. X-Wing
If a digit has exactly two possible cells in each of two rows, and those cells share the same two columns, the digit fills two corners of that rectangle. Remove it from the rest of both columns. Expert puzzles often need this.
Habits that make you faster
- Only start writing notes once scanning stops finding digits.
- After every placement, check the row, column and box it touches. New singles usually appear right there.
- Use the Hint button as a teacher: it names the technique and the unit involved.
- Play the daily Sudoku. The weekly rhythm from easy to expert builds skills gradually.
Stuck on a puzzle from a newspaper or app? Paste it into the Sudoku solver and step through it one explained move at a time.
Frequently asked questions
What is the best strategy for Sudoku?
Scan first, then use candidates. Scanning digit by digit finds most placements in easy puzzles. When scanning stalls, write pencil marks and look for hidden singles, then pointing pairs and naked pairs.
What is a hidden single?
A digit that can go in only one cell of a row, column or box, even if that cell has other candidates. Because the digit must appear somewhere in that unit, it goes in that one cell.
What is a naked pair?
Two cells in the same row, column or box that both have exactly the same two candidates, for example 3 and 7. Those two digits must go in those two cells, so you can remove 3 and 7 from every other cell in that unit.
What is a pointing pair?
When all candidates for a digit inside a box lie in one row (or column), that digit must be in that row within the box. You can remove it from the rest of that row outside the box.
How can I get faster at Sudoku?
Play daily, scan in a consistent order (1 through 9), and only write notes when scanning stops working. Speed comes from recognising patterns rather than checking every cell.