The Basic Sudoku Rules
Sudoku has three simple rules that govern the entire puzzle. Every sudoku puzzle, regardless of difficulty, follows these fundamental principles.
The Three Golden Rules of Sudoku:
Rule #1: Rows
Each horizontal row must contain all numbers from 1 to 9 exactly once. No number can repeat in the same row.
Rule #2: Columns
Each vertical column must contain all numbers from 1 to 9 exactly once. No number can repeat in the same column.
Rule #3: Boxes (3×3 Grids)
Each 3×3 box must contain all numbers from 1 to 9 exactly once. No number can repeat in the same box.
That's it! These three rules are all you need to solve any sudoku puzzle. Every decision you make must satisfy all three rules simultaneously.
Understanding the Sudoku Grid
Before diving into solving, let's understand the structure of a sudoku grid and how the rules apply.
Grid Structure
- 9×9 Main Grid: 81 total cells arranged in a square
- 9 Rows: Numbered 1-9 from top to bottom
- 9 Columns: Numbered 1-9 from left to right
- 9 Boxes: Each 3×3 sub-grid within the main grid
Box Numbering System
Box 1 | Box 2 | Box 3
Box 4 | Box 5 | Box 6
Box 7 | Box 8 | Box 9
Each box contains exactly 9 cells in a 3×3 arrangement
Cell Identification
Every cell in sudoku can be identified by its row and column position. For example, "R5C7" means Row 5, Column 7. This helps when discussing specific moves or strategies.
How to Start a Sudoku Puzzle
Every sudoku puzzle begins with some numbers already filled in - these are called "givens" or "clues." Your job is to fill in the remaining empty cells.
Understanding Given Numbers
- Pre-filled Clues: Numbers already placed in the grid
- Cannot Be Changed: Given numbers are permanent
- Starting Points: Use these to deduce where other numbers go
- Puzzle Difficulty: Fewer givens = harder puzzle
Your First Move
The Scanning Strategy
- Pick a number (start with 1)
- Scan each box to see which ones are missing that number
- For boxes missing the number, check which cells could contain it
- If only one cell is possible, write the number there!
- Repeat for numbers 2-9
Common Sudoku Rule Violations
Understanding what NOT to do is just as important as knowing the rules. Here are the most common mistakes beginners make.
❌ Rule Violations to Avoid
Duplicate in Row
Placing the same number twice in any horizontal row. Always check the entire row before placing a number.
Duplicate in Column
Placing the same number twice in any vertical column. Scan up and down the column before making your move.
Duplicate in Box
Placing the same number twice in any 3×3 box. This is often the trickiest to spot, so always double-check the box.
✅ Double-Check Strategy
Before placing any number, ask yourself:
- Is this number already in this row?
- Is this number already in this column?
- Is this number already in this 3×3 box?
If the answer to all three is "No," then you can safely place the number!
Advanced Sudoku Rules & Concepts
Once you master the basic rules, these advanced concepts will help you solve harder puzzles.
Logical Deduction Only
No Guessing Rule: Every number placement must be based on logical deduction. If you're not 100% certain, don't place the number. True sudoku solving never requires guessing.
Pencil Marks (Candidates)
For harder puzzles, you'll need to track possible numbers for each cell:
- Small Numbers: Write tiny numbers in cells to track possibilities
- Elimination: Remove candidates as you rule out possibilities
- Pattern Recognition: Look for cells with only one remaining candidate
Uniqueness Rule
Single Solution: Every valid sudoku puzzle has exactly one correct solution. If you find multiple solutions, there's an error in the puzzle or your solving.
Sudoku Difficulty Levels & Rules
Different difficulty levels require different applications of the basic rules, but the rules themselves never change.
Easy Sudoku Rules Application
- Many given numbers (36-46 clues)
- Scanning and basic elimination sufficient
- Usually solvable without pencil marks
- Multiple "naked singles" available at any time
Medium & Hard Sudoku Rules Application
- Fewer given numbers (28-35 clues)
- Requires pencil marks and advanced techniques
- Need to spot "hidden singles" and patterns
- More complex logical chains required
Expert Sudoku Rules Application
- Minimal given numbers (22-27 clues)
- Advanced pattern recognition essential
- Techniques like X-Wing, Swordfish needed
- Multiple logical paths to explore
🎯 Complete Rules of Sudoku Summary
Master the complete rules of sudoku with this comprehensive overview. Understanding all the rules of sudoku is essential for becoming a skilled player.
The Essential Rules of Sudoku
📋 Core Rules of Sudoku
The rules of sudoku are simple but must be followed precisely:
- Row Rule: Each row must contain numbers 1-9 exactly once
- Column Rule: Each column must contain numbers 1-9 exactly once
- Box Rule: Each 3×3 box must contain numbers 1-9 exactly once
These three rules of sudoku form the foundation of every puzzle solution.
Advanced Rules of Sudoku for Competitive Play
- Logic-Only Rule: The rules of sudoku require pure logic - no guessing allowed
- Single Solution Rule: Every valid sudoku following proper rules has exactly one solution
- Given Numbers Rule: Pre-filled numbers cannot be changed according to sudoku rules
- Pencil Mark Rule: Advanced rules of sudoku allow notation to track possibilities
- Elimination Rule: The rules of sudoku enable systematic elimination of impossibilities
Why Understanding Rules of Sudoku Matters
Mastering the rules of sudoku is crucial because:
- The rules of sudoku provide the logical framework for all solving strategies
- Understanding sudoku rules prevents common beginner mistakes
- Advanced rules of sudoku unlock complex solving techniques
- Knowing all rules of sudoku enables competitive puzzle solving
Rules of Sudoku in Different Variations
While the core rules of sudoku remain constant, variations may add additional constraints:
- Classic Sudoku: Standard rules of sudoku apply (rows, columns, boxes)
- Foursquare Sudoku: Same rules as classic, but only solve the center square
- Waterfall Sudoku: Endless scrolling mode with progressive difficulty and continuous gameplay madness!
Ready to Apply These Rules?
Now that you understand all the sudoku rules, it's time to put them into practice! Start with easy puzzles and gradually work your way up to harder difficulties.
Remember the Golden Rules:
Rows, Columns, and Boxes - each must contain 1-9 exactly once!
Start Practicing Sudoku →