How to Play Sudoku: A Quick Start Guide
You play Sudoku by filling a 9x9 grid so that each row, column, and 3x3 box contains the digits 1 through 9 exactly once. The goal is a single, logical solution. This guide will show you exactly how to start, what to look for, and how to avoid common beginner mistakes.
A standard Sudoku puzzle is a 9x9 grid divided into nine 3x3 sub-grids, or 'boxes'. Some numbers, called 'givens', are already filled in. Your job is to use logic, not guesswork, to deduce the correct position for every remaining number.
The Sudoku Grid & Rules
A Sudoku grid has 81 cells arranged in 9 rows and 9 columns. The thicker lines divide it into nine 3x3 regions, often called 'boxes' or 'blocks'. The three core rules are simple but must all be satisfied simultaneously: every row of 9 cells must contain 1-9, every column of 9 cells must contain 1-9, and every 3x3 box must contain 1-9. No digit can repeat within a row, column, or box.
How to Start Your First Puzzle
Begin with a 'beginner' or 'easy' rated puzzle. Your first move is a simple scan. Look for rows, columns, or boxes that already have many numbers filled in. Focus on finding the easiest placements first, which are often Naked Singles or Hidden Singles.
For example, if a row already has the numbers 1, 2, 3, 4, 5, 6, 7, and 8, the only digit missing is 9. Find the one empty cell in that row that can legally hold a 9 (checking its column and box too), and place it. This logical deduction is the essence of Sudoku.
- Start with the most populated row, column, or box.
- Look for the number 1, then 2, then 3, systematically scanning the grid.
Why and How to Use Pencil Marks
Pencil marks are small notes you write in the corners of empty cells to track possible candidates. As you solve, you eliminate possibilities. This is essential for progressing beyond the easiest puzzles. Our guide on Pencil Marking explains the full system.
To use them, look at an empty cell. Check its row, column, and 3x3 box. Any digit that already appears in those three zones is eliminated. Write the remaining possible digits (candidates) as small numbers in the cell. When only one candidate remains, you've found a number to place.
- Use a consistent notation style, like writing small digits in the cell's corners.
- Update pencil marks every time you place a new number.
The First Logical Techniques to Learn
After the initial scan, you'll use pencil marks to find logical patterns. The two most fundamental techniques are Naked Singles and Hidden Singles. A Naked Single is a cell where only one candidate remains in its pencil marks. A Hidden Single is a digit that can only go in one cell within a row, column, or box, even if other candidates are also present in that cell.
Mastering these two techniques will allow you to solve most 'easy' and many 'medium' puzzles. If you get stuck, our article on What to Do When Stuck offers a clear checklist to find your next move.
Common Beginner Mistakes to Avoid
New players often make a few key errors. The biggest is guessing. If you're not sure, use pencil marks instead. Another common error is forgetting to check all three constraints (row, column, box) for a cell, leading to an illegal placement that will break the puzzle later.
Also, avoid focusing on just one part of the grid. Placing a number in one area often reveals new placements in a completely different row or box. Keep scanning the entire puzzle after each placement.
Key Facts
- ▪Sudoku is played on a 9x9 grid subdivided into nine 3x3 boxes.
- ▪The sole rule is to fill the grid so each row, column, and 3x3 box contains digits 1-9 exactly once.
- ▪You solve Sudoku using pure logic and deduction; guessing is not required and often leads to errors.
- ▪The best starting strategy is to scan for rows, columns, or boxes that are almost complete.
- ▪Pencil marks are notes of possible numbers for a cell and are crucial for solving all but the simplest puzzles.
- ▪A Naked Single is a cell where only one digit can possibly fit based on its pencil marks.
- ▪A Hidden Single is a digit that has only one possible cell within a row, column, or box.
- ▪Every number you place gives you new information, so re-scan the entire grid frequently.
- ▪Most solving errors come from forgetting to check a cell's row, column, and box simultaneously.
- ▪Beginner puzzles can typically be solved using only Scanning, Naked Singles, and Hidden Singles.
Frequently Asked Questions
What is the one goal of Sudoku?
To fill the 9x9 grid so every row, every column, and every 3x3 box contains the digits 1 through 9, with no repeats in any of those three zones.
How do I start a Sudoku puzzle?
Do a quick scan. Look for any row, column, or 3x3 box that already has 8 numbers filled in. The 9th number must go in the single empty cell in that row, column, or box.
What are pencil marks and why use them?
Pencil marks are small notes of possible digits for an empty cell. They help you track options and see patterns, like Naked Singles, which are essential for solving.
Can I use the same number twice in a 3x3 box?
No. Each digit 1-9 must appear exactly once in every row, every column, and every 3x3 box. This is the core rule.
What if I get completely stuck?
Re-scan the entire grid with your pencil marks. Look for Hidden Singles. If still stuck, see our guide on What to Do When Stuck for a step-by-step process.
Is Sudoku a math game?
No. Sudoku is a logic puzzle. The digits 1-9 are just symbols; you could use letters or shapes. No arithmetic or calculation is involved.