How to Play Sudoku

Sudoku is a logic-based number puzzle. You are given a 9×9 grid, partly filled with numbers. Your goal is to fill in every empty cell so that the whole grid follows three simple rules — no guessing or math is required, only logic.

The Goal

The board is a 9×9 grid divided into nine 3×3 boxes. Fill the grid with digits from 1 to 9 so that each digit appears exactly once in every row, every column, and every 3×3 box.

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A starting Sudoku grid. The bold numbers are the given clues; you fill in the rest.

The 3 Rules

Rule 1 — Each row has 1 to 9

Look at any horizontal row. It must contain each of the numbers 1 through 9, with no repeats.

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Every row must contain the digits 1–9 exactly once.

Rule 2 — Each column has 1 to 9

The same is true for every vertical column: the digits 1 through 9 must each appear once.

123456789
Every column must contain the digits 1–9 exactly once.

Rule 3 — Each 3×3 box has 1 to 9

Finally, each of the nine 3×3 boxes (marked by the thicker borders) must also contain every digit from 1 to 9.

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Every 3×3 box must contain the digits 1–9 exactly once.

How to Solve — Step by Step

  1. Start with the easy wins. Scan the rows, columns and boxes for a spot where only one number can possibly fit.
  2. Use elimination. For an empty cell, cross off every digit that already appears in its row, its column, or its box. Whatever survives is a candidate.
  3. Find the "sole candidate". When elimination leaves only one possible digit for a cell, that digit must go there. Fill it in.
  4. Work in pencil. Note the small candidate numbers in the corners of cells (E-Sudoku has a Notes / pencil mode for this) so you don't lose track.
  5. Repeat. Every number you place removes candidates elsewhere, which usually unlocks the next cell.

Example: the sole candidate

In the grid below, the red cell's row and column (shaded blue) already contain 1, 2, 3, 5, 6, 7, 8 and 9. The only digit missing is 4 — so 4 is the only number that can go in that cell.

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The blue number (4) is forced: it is the only digit not already used in the shaded row and column.

Tips for Beginners

  • Start with the rows, columns or boxes that already have the most numbers filled in — they are the easiest to complete.
  • Never guess. Sudoku always has a single logical solution; if you are stuck, look again rather than gamble.
  • Focus on one number at a time. Ask "where can a 7 go in this box?" and scan for it across the grid.
  • Use the Notes feature to jot down candidates. This turns hard puzzles into a series of small, easy deductions.
  • Take your time. Higher difficulties reward patience, not speed.

Difficulty Levels

New to the game? Start with Easy Sudoku to learn the rules. When you are comfortable, work your way up through the levels — all the way to Evil Sudoku — or try a fresh challenge every day with Daily Sudoku. Prefer paper? You can also print Sudoku puzzles.

Ready to Play?

That's everything you need to get started. Pick a puzzle, apply the three rules, and enjoy training your brain. Browse all Sudoku puzzles and start solving now!