Sudoku Rules: How to play Sudoku
Sudoku is one of the world’s most popular logic puzzles, enjoyed by millions for its blend of simplicity and challenge. Whether you’re a complete beginner or looking to sharpen your skills, this comprehensive guide will teach you everything you need to know about playing Sudoku—from the basic rules to advanced tips and examples.
What is Sudoku?
Sudoku is a logic-based puzzle played on a 9x9 grid, divided into nine 3x3 blocks (also called boxes, regions, or subgrids). The objective is to fill the grid so that every row, column, and block contains the numbers 1 through 9 exactly once.
The Sudoku Grid Explained
This table shows you the relationship between the sudoku term and what it means. Understanding these terms is crutial to gaining a good understanding of how strategies and techniques work in Sudoku.
| Term | Description |
|---|---|
| Cell | A single square in the grid (81 total) |
| Row | A horizontal line of 9 cells (9 total) |
| Column | A vertical line of 9 cells (9 total) |
| Block | A 3x3 section of the grid (9 total) |
| House | Any row, column, or block (27 total) |
| Givens | The starting numbers provided in the puzzle |
Now that you know some of the essential Sudoku terms, let’s take a look at the rules that define the logic of a classic Sudoku puzzle.
Sudoku Rules
- Each row must contain the numbers 1–9, with no repeats.
- Each column must contain the numbers 1–9, with no repeats.
- Each 3x3 block must contain the numbers 1–9, with no repeats.
- Each cell can contain only one number.
- No guessing is required—every puzzle has a logical solution.
Step-by-Step: How to Play Sudoku
While you now have everything you need to start solving a Sudoku puzzle, it can be helpful to understand a simple strategy you can apply to solve your first Sudoku.
1. Scan for Obvious Numbers
- Look for rows, columns, or blocks that are nearly complete.
- Fill in any cells where only one number is missing.
2. Use the Process of Elimination
- For each empty cell, consider which numbers are already present in its row, column, and block.
- Eliminate those numbers as possibilities.
3. Use Pencil Marks (Candidates)
- Write small numbers in empty cells to keep track of possible candidates.
- As you fill in more cells, update your pencil marks.
4. Look for Singles
- Naked Single: A cell with only one possible candidate.
- Hidden Single: A candidate that appears only once in a row, column, or block.
5. Apply Advanced Techniques
- As puzzles get harder, use strategies like naked pairs, hidden pairs, X-Wing, and more. (See our Sudoku Techniques page for details.)
Example: Solving a Cell
Suppose you’re trying to fill a cell in row 1, column 2.
- The numbers already in row 1 are 3, 2, and 6.
- The numbers in column 2 are 9 and 8.
- The numbers in the top-left block are 3 and 9.
Possible candidates for this cell: 1, 4, 5, 7, 8
If you find that only one of these candidates fits (after checking all houses), you can fill it in.
Sudoku Solving Tips
- Start with easy puzzles to build confidence.
- Always use logic, not guessing.
- Update pencil marks as you fill in cells.
- Look for patterns like pairs, triples, and locked candidates.
- Take breaks if you get stuck—fresh eyes can help!
Sudoku Difficulty Levels
| Level | Description |
|---|---|
| Easy | Many givens, can be solved with basic logic and singles. |
| Medium | Fewer givens, may require pairs and simple elimination. |
| Hard | Even fewer givens, requires advanced techniques like X-Wing or Swordfish. |
| Evil | Minimal givens, demands expert strategies and deep logic. |
Frequently Asked Questions
Q: Can a Sudoku puzzle have more than one solution?
A: A proper Sudoku puzzle has only one unique solution.
Q: Is guessing allowed in Sudoku?
A: No. Every puzzle can be solved logically without guessing.
Q: What if I make a mistake?
A: Use an eraser or the undo feature (online) to correct errors. Double-check your logic before filling in a cell.
Play Sudoku Online
Ready to try your skills? Play Sudoku now!
Or, if you want to improve, check out our Sudoku techniques and strategy articles for more tips and examples.
More Resources
With this guide, you’re ready to tackle any Sudoku puzzle. Happy solving!