How to Play Sudoku — Complete Beginner's Guide (2026)

Last updated: February 2026 · By Khelnedo Games Team

Sudoku is the world’s most popular number puzzle, played by millions of people every day. Despite involving numbers, it requires zero math — just pure logic. This guide will teach you everything you need to start solving Sudoku puzzles from scratch.

What Is Sudoku?

Sudoku is a logic-based puzzle played on a 9x9 grid. The grid is divided into nine smaller 3x3 boxes (also called blocks or regions). When you start a puzzle, some cells already contain numbers — these are called givens or clues. Your job is to fill in the remaining empty cells.

The One Rule of Sudoku

Sudoku has exactly one rule:

Every row, every column, and every 3x3 box must contain the numbers 1 through 9 exactly once.

That is it. No addition, no subtraction, no math at all. You simply need to place numbers so that no number repeats in any row, column, or box.

Understanding the Grid

Here is how the 9x9 grid is organized:

• Rows — 9 horizontal lines running left to right (labeled Row 1 through Row 9)
• Columns — 9 vertical lines running top to bottom (labeled Column 1 through Column 9)
• Boxes — 9 regions of 3x3 cells (the thick-bordered squares on the grid)

Every cell belongs to exactly one row, one column, and one box. These three groups are called the cell’s peers or houses.

How to Solve Your First Puzzle: Step by Step

Step 1: Scan the Grid

Start by looking at the numbers already placed. Focus on rows, columns, or boxes that have the most numbers filled in — these are the easiest to complete.

Step 2: Look for Naked Singles

A Naked Single is the simplest Sudoku technique. Check an empty cell and eliminate every number that already appears in its row, column, and box. If only one number remains, that number must go in that cell.

Example: If a cell’s row contains 1, 3, 5, 7, 8, 9 and its column adds 2, 4, and its box adds 6, then only one possibility remains. Place it.

Step 3: Look for Hidden Singles

A Hidden Single occurs when a number can only go in one cell within a row, column, or box, even though that cell might have multiple candidates.

Example: Suppose the number 7 is missing from a row. If you check every empty cell in that row, and 7 is eliminated from all but one cell (by its column or box constraints), then 7 must go in that remaining cell.

Step 4: Use Pencil Marks

When you cannot immediately determine a cell’s value, write small candidate numbers (pencil marks) in the cell. This helps you:

• Keep track of possibilities
• Spot patterns later
• Avoid mistakes

In Sudoku Spark, you can toggle Notes Mode with a single tap to enter pencil marks.

Step 5: Repeat and Build

Keep scanning the grid after each number you place. Every new number you enter eliminates possibilities in its row, column, and box — which often reveals new Naked Singles or Hidden Singles.

Common Beginner Mistakes

• Guessing — Sudoku never requires guessing. If you are stuck, you are missing a logical deduction. Use hints.
• Forgetting boxes — Beginners often check rows and columns but forget the 3x3 box constraint.
• Not using pencil marks — Trying to keep track of candidates mentally leads to errors. Use notes mode.
• Rushing — Sudoku rewards careful observation. Take your time scanning before placing numbers.

Sudoku Difficulty Levels Explained

If you are just starting, begin with Easy puzzles. As techniques become natural, move up to Medium and beyond.

Basic Sudoku Strategies Summary

1. Scanning — Quickly check rows, columns, and boxes for missing numbers
2. Naked Single — Only one candidate remains in a cell after elimination
3. Hidden Single — A number can only go in one place within a row, column, or box
4. Pencil Marks — Track all candidates to spot patterns and avoid mistakes
5. Cross-Hatching — Check where a number can go in a box by eliminating rows and columns

What Makes a Good Sudoku Puzzle?

A well-crafted Sudoku puzzle has exactly one solution. It should be solvable through pure logic — no guessing required. The difficulty comes from how many steps of elimination are needed and how advanced the required techniques are.

Sudoku Spark generates puzzles that always have a unique solution and are solvable with logic appropriate to the selected difficulty level.

Next Steps

Ready to go beyond the basics? Check out our Sudoku Tips and Strategies guide to learn intermediate and advanced techniques like Naked Pairs, X-Wing, and more.

Or jump straight in — download Sudoku Spark and start your first puzzle with Smart Hints to guide you along the way.

Ready to Put These Skills to Work?

Download Sudoku Spark and start playing with smart hints, daily challenges, and 4 difficulty levels.