How to Play Sudoku
The rules in one minute, the two moves that solve most puzzles, and the strategies for hard grids.
The rules
A sudoku is a 9×9 grid split into nine 3×3 boxes. Some cells start filled in (the “givens”). Your job is to fill every empty cell with a digit from 1 to 9 so that:
- each row contains 1–9 exactly once,
- each column contains 1–9 exactly once, and
- each 3×3 box contains 1–9 exactly once.
That’s all. No arithmetic is involved; the digits could just as well be letters or colours. A proper sudoku has exactly one solution, so it can always be solved by logic, never by guessing.
The two moves that crack most puzzles
Almost every easy and medium sudoku can be finished with just two techniques. Step through them on a real grid:
Step 1 of 5
Pick an empty cell: the one outlined in the centre of the grid. Any number 1–9 could go there for now.
Naked single asks “what can go in this cell?” Hidden single asks “where can this number go in this row, column or box?” Switch between the two questions whenever you get stuck. Beginners often use only the first, but hidden singles usually turn up sooner.
Sudoku tips for beginners
- Start with the busiest rows, columns and boxes. A box with seven givens has only two gaps, so it’s almost done.
- Scan one digit at a time. Take every 1 on the board and see which boxes still need one and where it can go. Then 2s, then 3s. This “cross-hatching” finds hidden singles fast.
- Use pencil marks only when scanning dries up. Writing every candidate in every cell early on is slow; mark the stubborn cells.
- Never guess. If you’re about to guess, there’s a technique you haven’t spotted yet. The in-game Hint button on our daily sudoku will point to it and explain why it works.
Sudoku strategies for hard puzzles
When singles run out, these techniques remove candidates so that new singles appear. They’re listed roughly in the order you’ll need them.
| Strategy | What to look for | What it lets you do |
|---|---|---|
| Naked pair | Two cells in the same unit that both have exactly the same two candidates, e.g. {3,7} and {3,7}. | Those two digits must go in those two cells, so remove 3 and 7 from every other cell in that unit. |
| Hidden pair | Two digits that can only go in the same two cells of a unit. | Delete every other candidate from those two cells. |
| Pointing pair | Inside one box, a digit’s candidates all sit in one row (or column). | That digit must be in that row within the box, so remove it from the rest of the row outside the box. |
| Box/line reduction | Inside one row (or column), a digit’s candidates all sit in one box. | Remove the digit from the other cells of that box. |
| Naked triple | Three cells in a unit whose candidates, combined, are only three digits. | Remove those three digits from the rest of the unit. |
| X-wing | A digit that appears as a candidate in exactly two cells in each of two rows, and those cells line up in the same two columns. | Remove the digit from all other cells in those two columns (or rows, if you found it by columns). |
A method for any grid
- Cross-hatch every digit 1–9 for hidden singles in boxes.
- Check nearly full rows and columns for the last one or two digits.
- Pencil in candidates for the remaining cells.
- Look for naked singles, then pairs and pointing pairs. Each elimination can create a new single, so go back to step 1 after every placement.
Ready to try it? Today’s free daily sudoku comes in easy, medium and hard. Easy needs only naked singles, medium adds hidden singles, and hard calls for the strategies in the table.
Questions players ask
Do you need math to play sudoku?
No. Sudoku uses the digits 1–9 only as symbols. You never add or multiply anything.
What is the best way to start a sudoku?
Scan one digit at a time across the whole grid (cross-hatching) and place any digit that has only one possible cell in a box. Then look at nearly complete rows and columns.
How many clues does a sudoku need?
At least 17. In 2012, Gary McGuire and colleagues proved by exhaustive computer search that no 16-clue sudoku with a unique solution exists.
Is guessing allowed in sudoku?
It isn’t against the rules, but a well-made puzzle never requires it. Every cell can be deduced by logic.
Where did sudoku come from?
The modern puzzle was published as “Number Place” in Dell Magazines in 1979, then popularised in Japan by the publisher Nikoli, who named it sudoku, before spreading worldwide in 2004–2005.