Sudoku difficulty levels
| Level | Clues given | Techniques you will need |
|---|---|---|
| Easy | 37–38 | Singles: the only digit for a square, or the only square for a digit — with plenty of clues to start from |
| Medium | 29–30 | The same singles, with fewer clues and fewer obvious places to start |
| Hard | 26–30 | Pencil marks, pointing digits and pairs |
| Expert | 26–30 | More than pairs: longer chains of elimination across the grid |
Difficulty is set by the techniques a puzzle forces you to use, not by how many squares are empty — hard and expert puzzles here start with about the same number of clues, and the expert ones still need more. The clue counts are the middle 80% of puzzles from this site's generator.
About sudoku
Sudoku asks for no arithmetic, despite the numbers. The digits are just nine distinct symbols, and every puzzle is a pure logic problem: each row, column and 3×3 box holds each one exactly once. A properly made puzzle has exactly one solution and can be finished by reasoning alone — you never have to guess.
The puzzle is older than its name. It was first published in 1979 in an American puzzle magazine as Number Place, got the name sudoku from the Japanese publisher Nikoli in the 1980s, and went global after a British newspaper started running it in 2004.
What makes one harder than another is the reasoning it demands. Easy grids fall to scanning: look at a row, a column and a box, and there is only one place a digit can go. Harder grids need pencil marks, and the work shifts from placing digits to ruling them out. How to solve sudoku walks through each technique in the order you will need them, and sudoku for beginners covers the rules and the first move if you have never played.
Every puzzle here keeps your pencil marks, undo and progress if you close the tab, and a hint is there if you are stuck. Every solve is scored and your best goes on the leaderboard. Start at easy if you are new — or go straight to expert and see whether you can finish one without a hint.
Frequently asked questions
Which sudoku level should I start with?
Easy, if you have never played. Every easy puzzle can be solved by scanning alone, so it teaches you the rules without needing pencil marks.
Do you need to guess in sudoku?
No. A proper sudoku has exactly one solution and can always be finished by logic. If you are guessing, there is a technique you have not spotted yet — how to solve sudoku covers them.
What is the fewest clues a sudoku can have?
Seventeen. A computer search completed in 2012 proved that no puzzle with sixteen clues has a single solution. More in does every sudoku have one solution?
How many sudoku grids are there?
About 6.67 sextillion completed grids — 6,670,903,752,021,072,936,960 to be exact — or roughly 5.5 billion if you count grids that are the same up to rotation, reflection and relabelling as one.
Do I need to sign up or download anything?
No. Sudoku runs in the browser and plays fully signed out. Signing in with Google only keeps your scores on the leaderboard and your progress across devices.