How to play Sudoku

The rules

The board is a 9×9 grid split into nine 3×3 boxes. Some squares start with a number. Fill every empty square so that each row, each column and each 3×3 box contains the digits 1 to 9 exactly once.

A well-made puzzle has exactly one solution, and you never need to guess. If you find yourself guessing, there is a technique you have not spotted yet.

Playing in Bill’s Sudoku

• Tap a square, then a number piece to place it.
• Turn on Notes to pencil small candidate numbers into a square. Notes clear themselves when you place a number.
• Undo takes back your last move, Erase clears the selected square, and Hint fills in a correct number when you are truly stuck.
• With Mark wrong numbers on, a number that does not belong turns red as soon as you place it. Switch it off if you prefer to find mistakes yourself.
• For a change of pace, turn on Kanji numbers and the pieces show 一 二 三 instead of 1 2 3.

Easy and Medium are free in your browser. Every level keeps your ten fastest solves on your device.

Technique 1: scanning

Pick a digit, say 5, and look at one box. For every 5 already in the rows and columns that pass through that box, mentally cross out that row or column inside the box. If only one empty square is left, the 5 goes there. This is often called cross-hatching, and it solves most of an Easy puzzle on its own.

Work digit by digit, 1 to 9, across all nine boxes. Then do it again: every number you place opens up new eliminations.

Technique 2: singles

There are two kinds of single, and between them they solve every Easy and most Medium puzzles.

• Naked single. A square where only one digit is still possible, because the other eight already appear in its row, column or box.
• Hidden single. A digit that has only one possible square left in a row, column or box, even if that square could hold other digits too.

When scanning stops working, fill in notes for the whole board. Singles become easy to see once the candidates are written down.

Technique 3: pairs and pointing

• Naked pair. If two squares in the same row, column or box both have exactly the same two candidates, say 3 and 7, then those two digits must go in those two squares. Remove 3 and 7 from every other square in that unit.
• Pointing. If all the possible places for a digit inside one box lie on a single row (or column), that digit must be in that row within the box. Remove it from the rest of the row outside the box.
• Box/line reduction. The reverse: if a digit’s only places in a row all sit inside one box, remove it from the rest of that box.

These three ideas unlock most Hard puzzles. After every elimination, look for new singles.

Tips for faster solves

• Start with the digits that already appear most often on the board. They have the fewest places left.
• Keep notes tidy. A wrong note is worse than no note.
• When you place a number, check its row, column and box straight away for a new single.
• If you get stuck, step away for a minute. Fresh eyes spot the obvious.

Play a new puzzle every day

Our Daily Sudoku gives everyone the same puzzle each day: Easy on Monday and Tuesday, Medium on Wednesday and Thursday, and Hard from Friday to Sunday. Solve it to build your streak, then share your time.

Updated 2 November 2026. Written by JPAM Studio, the makers of Bill's Sudoku.