How to play Sudoku
A Sudoku grid has 81 squares arranged in 9 rows, 9 columns and 9 boxes of 3x3. Some squares start with numbers. Fill in the rest so that:
- every row contains the digits 1 to 9 exactly once,
- every column contains the digits 1 to 9 exactly once, and
- every 3x3 box contains the digits 1 to 9 exactly once.
That is the whole rulebook. No math is involved. The numbers are just symbols, and the puzzle is pure logic.
Controls
- Computer: click a square, then type a number. Arrow keys move around, Backspace clears, and N switches pencil (notes) mode on and off. Ctrl/Cmd + Z undoes.
- Phone or tablet: tap a square, then tap a number on the pad below the grid. Tap Notes to switch to pencil marks.
The small number under each digit on the pad shows how many of that digit are still missing from the board.
Helpful features
- Unique puzzles, every time. Each puzzle is generated fresh and verified by a solver to have exactly one solution, so it can always be solved by logic without guessing.
- Honest difficulty levels. Every puzzle is graded by the techniques it takes. Easy and Medium need only singles, Hard needs pairs or pointing, and Expert needs advanced moves like the X-Wing.
- Mistake highlighting. A wrong number is shown in red and counted, so you can decide how strict to be with yourself.
- Smart notes. When you place a correct number, the matching pencil marks disappear from its row, column and box automatically.
- Hints. Stuck? Select a square and press Hint to fill it in.
- Auto-save. Close the tab and your puzzle is still here when you come back on the same device.
How to solve: the basic routine
- Scan for singles. Pick a digit and check each box: if the digit can only go in one square of that box, place it.
- Check crowded rows and columns. A row with seven or eight numbers filled in usually gives up its last squares quickly.
- Add pencil marks once scanning dries up. Write every possible candidate in each empty square.
- Look for pairs. If two squares in a row can only be 3 or 7, no other square in that row can be 3 or 7.
- Repeat. Every number you place creates new chances elsewhere.
Hard and Expert puzzles need more advanced techniques such as pointing pairs and the X-Wing. Our Sudoku strategies guide explains each one with worked examples, from your first puzzle to the toughest grids.
Pro tip: When you are stuck, pick the digit that already appears most often on the board and hunt for its remaining spots. It is the digit with the fewest possible places left.
Where Sudoku came from
The puzzle as we know it was first published in 1979 in Dell Magazines in the United States under the name "Number Place", credited to puzzle designer Howard Garns. It became popular in Japan in the 1980s, where the publisher Nikoli gave it the name Sudoku, and it swept the rest of the world in the mid-2000s after appearing in British newspapers. Today it is one of the most popular logic puzzles on the planet.
Sudoku FAQ
Does every puzzle have a unique solution?
Yes. Each puzzle is generated and then checked by a solver to make sure exactly one solution exists, so you never have to guess.
What is the difference between the difficulty levels?
Every puzzle is graded by the techniques it needs. Easy and Medium can be solved with singles alone, Hard needs pairs or pointing, and Expert needs advanced techniques such as an X-Wing.
What are pencil marks?
Small notes of the numbers that could still go in a cell. They make it much easier to spot pairs and other patterns.