How to play Sudoku
Here’s how to play Sudoku: fill every empty square of the 9×9 grid with a digit from 1 to 9 so that each row, each column and each of the nine 3×3 boxes contains every digit exactly once. It’s free to play online in your browser, with easy, medium and hard puzzles, pencil notes and undo.
There’s a timer, a fastest-time leaderboard for each difficulty, and a daily puzzle that’s the same for everyone. Every puzzle has exactly one solution and never needs guessing. Below you’ll find the rules, some solving tips and answers to common questions.
The basics
Fill every empty square so that each row, each column and each 3×3 box contains the digits 1 to 9 exactly once.
The goal
- The digits already on the grid are the givens: they can’t be changed.
- No digit can appear twice in the same row, column or 3×3 box.
- Every puzzle has exactly one solution and can be solved by logic, so you never have to guess.
Playing
- Phone or tablet: tap a square, then tap a number on the pad. Erase clears the square and Undo takes back your last move.
- Notes: switch Notes on to pencil small digits into a square. When you place a digit, its notes in the same row, column and box are cleared for you.
- Keyboard: type 1–9, move with the arrow keys, Backspace or Delete to erase, N for notes and Z to undo.
- Squares that break the rules (the same digit twice in a line or box) turn red. Switch on Check to see wrong digits as you go.
Difficulty
- Easy: every move is a square with only one possible digit.
- Medium: you’ll also need to spot where a digit can only go in one place in a row, column or box.
- Hard: pairs and “pointing” digits come into it.
The timer and the leaderboard
- The clock runs while you play. Pausing hides the grid so you can’t study it with the clock stopped. The game also pauses if you switch to another tab or app, and a puzzle you leave is saved so you can carry on.
- When you finish, the server checks your grid. Your fastest time on each difficulty goes on the leaderboard.
- On the days Sudoku is the daily challenge, everyone gets the same puzzle and the fastest time tops that day’s board.
Beginner tips
- Start with the squares that have the most clues around them. Look for a row, column or box that’s nearly full, and work out which digit is missing.
- Scan for each digit in turn. Pick a number, find where it already is, and see where it can still go in each box: often only one square is left.
- Use pencil notes when you’re stuck. Write the possible digits in a square, and when a digit is placed its notes in the same row, column and box are cleared for you. Naked pairs and “pointing” digits (a digit stuck in one line of a box) unlock the hard puzzles.
Frequently asked questions
What are the rules of Sudoku?
Every row, every column and every 3×3 box must contain the digits 1 to 9 exactly once. The digits already on the grid (the givens) can’t be changed.
How do I play Sudoku on a phone?
Tap a square, then tap a number on the pad. Switch on Notes to pencil in possible digits, use Erase to clear a square and Undo to take back a move. On a keyboard you can type the digits, use the arrow keys to move and press N for notes.
Do the puzzles ever need guessing?
No. Every puzzle has exactly one solution and can be solved by logic. Easy puzzles only need the obvious squares, medium ones need you to spot where a digit can only go in one place, and hard ones need techniques such as pairs and locked candidates.
How is it ranked?
By your fastest time on each difficulty. A finished grid is checked by the server before it counts.
What is the daily Sudoku?
On the days that Sudoku is the daily challenge, everyone gets the same puzzle and the fastest time tops that day’s board. New challenges start at midnight GMT.
Is it free to play Sudoku?
Yes. Sudoku is free to play in your browser, with nothing to download.
Ready to play Sudoku?
It’s free and works in your browser — no download. Start against Trevor, the friendliest opponent, and sign up free to climb the ladder of ten computer players all the way to Pete.
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