Basic Sudoku Rules

Master the fundamental rules that make Sudoku the world's most popular number puzzle game.

The Sudoku Grid

Sudoku is played on a 9×9 grid divided into nine 3×3 sub-grids (also called "boxes" or "regions"). The grid comes with some numbers already filled in - these are called "givens" or "clues".

  • • 9×9 Grid: 81 cells total
  • • Nine 3×3 Boxes: Each contains 9 cells
  • • Given Numbers: Pre-filled clues to start the puzzle
5
3
7
6
1
9
5
9
8
6
8
6
3
4
8
3
1
6
8
4
1
9
8
7
9
6
2
8
4

Example Sudoku puzzle showing given numbers (shaded cells)

The Three Fundamental Rules

Rule 1: Complete All Rows

Each horizontal row must contain all numbers from 1 to 9, with no repetitions.

1
2
3
4
5
6
7
8
9

✓ Valid row - contains all numbers 1-9

Rule 2: Complete All Columns

Each vertical column must contain all numbers from 1 to 9, with no repetitions.

1
2
3
4
5
6
7
8
9

✓ Valid column - contains all numbers 1-9

Rule 3: Complete All 3×3 Boxes

Each of the nine 3×3 boxes must contain all numbers from 1 to 9, with no repetitions.

1
2
3
4
5
6
7
8
9

✓ Valid 3×3 box - contains all numbers 1-9

How to Play

Your Goal

Fill every empty cell in the 9×9 grid with a number from 1 to 9, following the three fundamental rules. A puzzle is complete when every row, column, and 3×3 box contains all digits 1-9.

Getting Started

  1. 1 Look for cells where only one number can fit
  2. 2 Use process of elimination to narrow down possibilities
  3. 3 Check your work frequently to avoid errors
  4. 4 Be patient and systematic in your approach

💡 Beginner Tip

Start by looking for rows, columns, or boxes that are almost complete. These often reveal obvious number placements that can help you get started.

⚠️ Important

Never guess! Every number you place should be based on logical deduction. Guessing can lead you down the wrong path and make the puzzle unsolvable.

Difficulty Levels

Easy

More given numbers, simpler logic required

Medium

Moderate number of clues, requires basic techniques

Hard

Fewer clues, advanced strategies needed

Expert

Very few clues, complex reasoning required

Back to Rules Next: Obvious Singles

Ready to Apply These Rules?

Now that you understand the basic rules, try playing a game to practice!

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