How to Play Sudoku: Rules, Strategies, and Solving Techniques
Sudoku is one of the world's most popular logic puzzles. Despite using numbers 1–9, it requires zero math — only reasoning and pattern recognition. This guide covers the rules, beginner strategies, and advanced techniques to solve any puzzle.
The Rules of Sudoku
A standard Sudoku grid is 9×9 squares, divided into nine 3×3 boxes. The goal is to fill every cell so that:
- Every row contains the digits 1–9 exactly once
- Every column contains the digits 1–9 exactly once
- Every 3×3 box contains the digits 1–9 exactly once
A valid puzzle has exactly one solution. Given numbers are called "givens" or "clues" — you cannot change them.
Difficulty Levels
| Level | Givens | Techniques Needed | |-------|--------|-------------------| | Easy | 36–45 | Basic elimination | | Medium | 27–35 | Naked pairs, pointing pairs | | Hard | 20–26 | X-wing, swordfish | | Expert | <20 | Chains, guessing |
Beginner Strategy: Elimination
The most fundamental technique is simple elimination.
Step 1: Pick an empty cell.
Step 2: List which numbers 1–9 are already in its row, column, and box.
Step 3: The remaining numbers are candidates. If only one candidate remains, place it.
Example: A cell shares its row with 1,3,4,7, its column with 2,5,8, and its box with 6,9. The only missing number is — none, check again. If 1,2,3,4,5,7,8,9 are all eliminated, the answer is 6.
Scanning: The Full Grid View
Instead of cell-by-cell, scan an entire number across the grid.
Pick the number 7. Find all rows and columns that already contain 7. In each remaining row/column, use the existing 7 positions to eliminate boxes where 7 can't go. Often this forces 7 into a single cell in a box.
This is called cross-hatching and is the fastest technique for easy puzzles.
Naked Singles and Hidden Singles
Naked single: A cell with only one possible candidate. Fill it immediately.
Hidden single: A number that can only go in one cell within a row, column, or box — even though that cell might have multiple candidates. Scan each box: if 4 only fits in one cell of that box, place it there regardless of other candidates.
Naked Pairs
If two cells in the same row, column, or box both contain exactly the same two candidates (e.g., both show 7), those two numbers must go in those two cells. You can eliminate 3 and 7 as candidates from all other cells in that row, column, or box.
Pointing Pairs
If a candidate in a box only appears in one row or column of that box, you can eliminate that candidate from the rest of that row or column outside the box.
Example: If 5 only appears in the top row of the top-left box, then 5 cannot appear elsewhere in that top row.
The X-Wing Technique (Advanced)
X-Wing applies when a candidate appears in exactly two cells in each of two rows, and both rows have the candidate in the same two columns. You can eliminate that candidate from all other cells in those two columns.
This forms an "X" shape across the grid — hence the name.
Tips for Beginners
- Start with easy puzzles — build confidence before tackling hard ones
- Use pencil marks — write small candidate numbers in cell corners
- Don't guess on easy/medium — logic always suffices
- Scan the whole puzzle before filling any cell — a global view prevents mistakes
- Check rows, columns, and boxes every time you place a number
Common Mistakes
- Placing the same number twice in a row/column/box
- Erasing a correct number because it "seems wrong"
- Not updating pencil marks after placing a number
- Guessing when you haven't exhausted logical options
Practice Online
Use our free Sudoku calculator to generate Easy, Medium, or Hard puzzles with a built-in solver. Stuck on a puzzle? Click Solve to see the complete solution.
Sudoku rewards patience and methodical thinking. Start with easy puzzles, master elimination, then gradually learn more advanced techniques as your skills grow.