Sudoku Rules Guide
Sudoku Rules: How to Play Sudoku Correctly
Learn the complete Sudoku rules in a simple way: every row, column, and 3×3 box must contain the numbers 1 to 9 without repeating any number.
The One Rule to Remember
Place numbers 1 to 9 so each number appears only once in every row, column, and 3×3 box.
Rows
Each horizontal row must contain 1 to 9 with no repeated number.
Columns
Each vertical column must also contain 1 to 9 without duplicates.
3×3 Boxes
Each small 3×3 box must contain every number from 1 to 9 once.
What Are the Rules of Sudoku?
Sudoku is a logic puzzle played on a 9×9 grid. The goal is to fill every empty cell with a number from 1 to 9. The puzzle starts with some numbers already given as clues.
A move is correct only when the number does not repeat in the same row, column, or 3×3 box. This is the main rule that controls the entire puzzle.
Although Sudoku uses numbers, it is not a math game. You do not calculate totals. You use logic, scanning, and elimination to decide where each number can go.
The 3 Main Sudoku Rules
Each Row Must Contain 1 to 9
A row is a horizontal line across the Sudoku grid. Every row must include each number from 1 to 9 exactly once. If a row already has a 7, another 7 cannot go anywhere in that same row.
Each Column Must Contain 1 to 9
A column is a vertical line from top to bottom. Every column must contain numbers 1 to 9 without repeating. Before placing a number, always check the column.
Each 3×3 Box Must Contain 1 to 9
The 9×9 grid is divided into nine smaller 3×3 boxes. Each box must also contain all numbers from 1 to 9 once. A number cannot repeat inside the same box.
What Makes a Sudoku Move Legal?
✅ Legal Move
A move is legal when the number is not already used in that cell’s row, column, or 3×3 box.
❌ Illegal Move
A move is illegal when the same number already appears in the row, column, or 3×3 box connected to that cell.
Simple Check Before Placing a Number
- 1. Check the row. Is the number already there?
- 2. Check the column. Is the number already there?
- 3. Check the 3×3 box. Is the number already there?
- 4. If the answer is no for all three, the move follows the basic Sudoku rules.
Sudoku Grid Explained
How to Start a Sudoku Puzzle Using the Rules
Look for the Most Filled Rows, Columns, or Boxes
Areas with many given numbers are easier to solve because fewer numbers are missing.
Use Elimination
Remove numbers that already appear in the same row, column, or 3×3 box. The remaining possible numbers are your candidates.
Place Only Confirmed Numbers
If only one number can fit in a cell, place it. If you are not sure, use notes instead of guessing.
Common Sudoku Rule Mistakes
❌ Checking Only the Row
A number may look correct in a row but still break the column or box rule. Always check all three areas.
❌ Forgetting the 3×3 Box
Many beginner mistakes happen because players check rows and columns but forget the smaller 3×3 box.
❌ Guessing Too Early
Guessing can fill the grid faster at first, but one wrong guess can make the whole puzzle confusing later.
❌ Ignoring Given Clues
The starting numbers are fixed clues. Use them carefully because every correct answer must fit around them.
Sudoku Rules vs Sudoku Strategy
Sudoku rules tell you what is allowed. Sudoku strategy tells you how to find the correct numbers faster.
For example, the rule says a number cannot repeat in a row. A strategy uses that rule to eliminate impossible cells and find where a number must go.
After you understand the rules, continue with our Sudoku Strategies guide to learn scanning, elimination, hidden singles, naked singles, and better note-taking.
Best Sudoku Level After Learning the Rules
🟢 Easy Sudoku
Best for beginners who just learned the rules and want simple practice.
🔥 Daily Sudoku
Good for building a daily habit, keeping streaks, and improving over time.
🟡 Medium Sudoku
Try Medium when Easy Sudoku feels comfortable and you can solve without guessing.
🟠 Hard Sudoku
Try Hard after you understand notes, candidates, and more advanced solving patterns.
Frequently Asked Questions
What are the basic rules of Sudoku?
Fill every empty cell with a number from 1 to 9. Do not repeat the same number in any row, column, or 3×3 box.
Can a Sudoku puzzle have repeated numbers?
No. A completed Sudoku puzzle cannot repeat the same number in a row, column, or 3×3 box.
Do you need math to play Sudoku?
No. Sudoku uses numbers, but it is a logic puzzle. You do not need to calculate anything.
Is guessing allowed in Sudoku?
Guessing is not the best way to solve Sudoku. Good solving comes from logic, checking, and elimination.
What is a 3×3 box in Sudoku?
A 3×3 box is one of the nine smaller sections inside the Sudoku grid. Each box must contain numbers 1 to 9 once.
Now Practice the Sudoku Rules
The fastest way to understand Sudoku rules is to play beginner-friendly puzzles and check every row, column, and 3×3 box as you solve.