How to play Sudoku: rules and tips
Sudoku is a number puzzle on a 9×9 grid. Some numbers are printed from the start, and you fill in the rest so that no number repeats in a row, a column or a box. You need no maths, only patience and a little logic. An easy puzzle takes five to ten minutes.
The rules
- Fill every empty square with a number from 1 to 9.
- Each row has every number exactly once. Nine squares, nine numbers, no repeats.
- Each column has every number exactly once, top to bottom.
- Each box has every number exactly once. The thick lines split the grid into nine 3×3 boxes.
Every puzzle has exactly one answer, and you can always reach it by logic alone. The printed numbers never change; only the empty squares are yours to fill.
Controls
- Tap a square to select it, then tap a number on the pad below the board. Tap the same number again to take it out.
- Or pick the number first: select a printed number, tap a number on the pad, then tap every square where it goes. Tap the number again to stop.
- Notes switches the pad to pencil marks, so you can write the numbers a square could still hold. Erase clears the selected square and Undo steps back one move.
- On a keyboard: arrow keys move, a digit writes a number, Shift plus a digit writes a note, N switches notes on and off, and Backspace erases.
- Hint highlights the next step you can prove and explains why.
- The selected square lights up its row, column and box, and every square with the same number. A number that repeats in a row, column or box gets a red ring. With Tidy notes on (in Settings), writing a number removes it from the notes it can see.
Five techniques that solve every board
Every sudoku here can be finished with the moves below. Easy puzzles need only the first two. Medium ones add notes, pointing and pairs. Hard ones, in the practice sets, need an X-wing or a wing now and then.
All eight sudoku techniques, with worked boards, from the hidden single to the XY-wing.
1. Scan a box for one number
Pick a number and a box that lacks it. Every copy of that number elsewhere rules out its whole row and column. Often only one square of the box is left, and the number goes there. Work through the numbers 1 to 9, box by box.
2. The last number of a square
Look at one empty square and list what its row, column and box already hold. When eight of the nine numbers are used, the ninth goes in. A row, column or box with only one empty square is the quickest case of all.
3. Pencil in the options
When scanning stops giving numbers, write in each empty square the numbers it could still hold. Notes turn the rest of the puzzle into crossing out: each number you place removes itself from the notes in its row, column and box.
4. Pointing and pairs
If a number's notes in a box all sit in one row, the box's copy is in that row, so the rest of the row can't hold it. And if two squares of a row can only be the same two numbers, those two numbers are used up there: cross them out of the rest of the row.
5. The X-wing
On hard boards, look for a number that fits only two squares in each of two rows, in the same two columns. One copy of each column has to come from those rows, so no other square in those columns can hold that number.
Easy, medium and hard sudoku
Monday to Thursday the daily sudoku is easy: you can finish it by scanning alone. Friday is a light medium and the weekend a full medium, where notes, pointing and pairs come in. Hard puzzles live in the practice sets, so they never break your streak.
Want another one? Play an easy sudoku, a medium sudoku or a hard sudoku, or start small with a 4×4 and a 6×6.
Questions
Can I play sudoku online for free?
Yes. The daily sudoku, every past day in the archive and all the practice puzzles are free in your browser. There is no sign-up and no app to install.
How do you solve a sudoku?
Start with the numbers that appear most often. For each one, scan the boxes that lack it and see where it still fits. When that stops, write notes in the empty squares and look for squares with one note left, pairs and pointing notes.
Do I need to be good at maths?
No. The numbers are only nine different symbols; you never add them up. Letters or colours would work just as well.
Can a puzzle need a guess?
No. Before a puzzle is published, a solver works through it with the techniques above, step by step. If it ever has to guess, the puzzle is thrown away. The grade says which techniques it needs.
What makes a sudoku easy or hard?
Not the number of printed numbers, but the hardest step it needs. An easy one needs only scanning. A medium one needs notes, pointing and pairs. A hard one needs a pattern such as the X-wing at least once.
How many numbers does a sudoku start with?
Our easy puzzles start with about 36 numbers and the harder ones with 22 to 30. The printed numbers are placed symmetrically, as in a newspaper sudoku.
When does a new puzzle come out?
At midnight in your own time zone. Monday to Thursday are easy, Friday is a light medium and the weekend is medium. Every past daily stays in the archive.
Can I print sudoku puzzles?
Yes. The printable page has this week's daily puzzles and a pack of easy, medium and hard sudoku, two or four to a page, with the answers at the end.