How to Play Sudoku: A Complete Beginner's Guide

Sudoku is one of the most popular puzzles in the world, but if you have never played before, staring at a grid of numbers can feel intimidating. The good news is that Sudoku is simpler than it looks. You do not need to be good at math. You just need logic and patience.

Here is everything you need to know to solve your first Sudoku puzzle.

The Basic Rules

A Sudoku puzzle is a 9x9 grid divided into nine 3x3 boxes. Some cells are pre-filled with numbers (called "givens"). Your job is to fill in the empty cells so that:

1. Every row contains the numbers 1 through 9 (no repeats)
2. Every column contains the numbers 1 through 9 (no repeats)
3. Every 3x3 box contains the numbers 1 through 9 (no repeats)

That is it. Three rules. No math, no guessing (in a properly designed puzzle), just pure logical deduction.

Getting Started: Scanning

The first technique every beginner should learn is scanning. Look at what numbers are already placed and figure out where other numbers must go based on elimination.

Row and column scanning: Pick a number (say, 5). Look at every row and column that already has a 5. For each 3x3 box that is missing a 5, check which cells are still available. If only one cell in that box can possibly hold a 5 (because all other cells are blocked by existing 5s in the same row or column), write it in.

Box scanning: Pick a 3x3 box and list which numbers are missing. Then check each empty cell in that box against its row and column to see which numbers it can hold.

Beginner Techniques

Naked Singles

A naked single is when a cell can only contain one possible number. Look at an empty cell, check its row, column, and box, and eliminate every number that already appears. If only one number remains, that is your answer.

For example, if a cell's row contains 1, 3, 5, 7, 8, its column contains 2, 4, 6, 9, and its box contains 1, 2, 3, then the only remaining number is... work through the elimination and you will find it.

Hidden Singles

A hidden single is when a number can only go in one place within a row, column, or box, even though that cell might have multiple candidates. If you are tracking possible numbers for each cell, look for a number that appears as a candidate in only one cell of a group.

Pencil Marks

As puzzles get harder, keeping track of candidates in your head becomes impossible. Use pencil marks to write small candidate numbers in each empty cell. Most digital Sudoku games (including ours) support pencil marks. This turns Sudoku from a memory challenge into a pure logic puzzle.

Common Mistakes

Guessing. Proper Sudoku puzzles never require guessing. If you feel stuck, there is a logical deduction you have missed. Go back and check your pencil marks.

Forgetting to check all three constraints. Every cell is governed by its row, column, and box. Beginners sometimes forget to check one of these, leading to errors.

Not scanning systematically. Random scanning misses things. Work through numbers 1 through 9 in order, scanning the entire grid for each number.

Difficulty Levels

• Easy puzzles have many givens and can be solved entirely with scanning and naked singles
• Medium puzzles require hidden singles and careful pencil marking
• Hard and Expert puzzles need advanced techniques like naked pairs, pointing pairs, and X-wings

Start with easy puzzles and work your way up. There is no shame in easy mode because even experienced players use easy puzzles as warm-ups.

Where to Play

Play Sudoku free in your browser with multiple difficulty levels, pencil marks, and automatic error checking. If you enjoy number logic puzzles, also try KenKen (Sudoku meets arithmetic), Kakuro (crossword-style number puzzles), and Futoshiki (Sudoku with inequality constraints).

All free at PlayBrain with no download required.