How to Play Sudoku: Rules and a Beginner's Method

Learn the rules of Sudoku and a simple scanning method to solve your first grids, with the pencil-note habit that makes harder puzzles click.

Updated 5 min read By CodingEagles
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To play Sudoku, fill the 9x9 grid so that every row, every column and each of the nine 3x3 boxes holds the digits 1 to 9 with no repeats. That single rule is the whole game. You start with some cells already filled, and you work out the rest by logic. Open the Sudoku board and you can try the method below on a live puzzle.

The one rule, three ways

Every empty cell answers to three constraints at once:

  1. Its row already contains some of the digits 1 to 9. Those are out.
  2. Its column contains some too. Also out.
  3. Its 3x3 box contains some. Out as well.

Whatever digit is not banned by any of the three can legally go in that cell. When only one digit survives all three checks, you have found a forced move.

A scanning method that works

The fastest way in for a beginner is to hunt one digit at a time.

Pick a digit that already appears several times on the board, say the 5. Look at each 3x3 box that is still missing a 5. The rows and columns that already contain a 5 cut through that box and forbid those cells. Often this leaves only one open cell in the box, and that is where the 5 must go. Work through every box for the 5, then move to the next digit.

This is called cross-hatching, and on an easy grid it solves most of the board on its own.

When scanning stalls, pencil in notes

Harder puzzles reach a point where no single cell is forced by scanning. This is where notes earn their keep. In each empty cell, pencil in every digit that is still legal there. The Sudoku board has a Notes mode for exactly this.

Once the candidates are written down, two simple patterns clear cells:

  • A cell with only one candidate left is forced.
  • A digit that can go in only one cell of a row, column or box is forced there, even if that cell has other candidates pencilled in.

Filling a forced cell removes that digit from its row, column and box, which often forces the next cell. The grid unwinds from there.

A few habits that help

  • Always work the constraint with the fewest blanks first. A box with one empty cell is a free move.
  • Update your notes the moment you place a digit. Stale notes lead to mistakes.
  • If you are stuck, switch from scanning by digit to scanning by cell, looking for the cell with the fewest candidates.

Once these feel natural, the named techniques in Sudoku solving techniques are the next step up to Hard and Expert grids. To put the method into practice now, open the Sudoku board and start on Easy with notes turned on.

Frequently asked questions

What are the basic rules of Sudoku?
Fill the 9x9 grid so every row, every column and each of the nine 3x3 boxes contains the digits 1 to 9 exactly once. Some cells are filled in to start. There is no arithmetic; it is placement logic, and each puzzle has one correct answer.
Do you need to be good at maths to play Sudoku?
No. The digits 1 to 9 are just symbols, and you never add or multiply them. You could replace them with nine different shapes and the puzzle would work the same. Sudoku is about logic and pattern spotting, not calculation.
What is the easiest way to start a Sudoku puzzle?
Scan for the digit that already appears most often. For each box still missing it, see whether the rows and columns crossing that box rule out every cell but one. When only one cell is left, that digit goes there. Repeat for the next most common digit.

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Sudoku Solving Techniques: From Naked Singles to X-Wings Once scanning stops working, named techniques take over. Here are the ones that actually solve Hard and Expert grids, in the order you should reach for them. The Benefits of Puzzle Games for Your Brain Puzzle games are sold as brain training. The honest version is more modest and more useful: here is what Sudoku, Minesweeper and the rest really exercise.