How to Play Sudoku: Complete Beginner's Guide

By Sudokuzio · Beginner · 8 min read

Sudoku is one of the world's most popular puzzles — and for good reason. It requires no maths, no language, and no special knowledge. All you need is logic and patience. This guide will take you from complete beginner to solving your first puzzle confidently.

What Is Sudoku?

Sudoku is a number-placement puzzle played on a 9×9 grid. The grid is divided into nine 3×3 boxes. Some cells are already filled with numbers from 1 to 9. Your job is to fill in the empty cells so that every row, every column, and every 3×3 box contains each digit from 1 to 9 exactly once.

That's it. There are no tricks, no catches. Sudoku is pure logic. A well-made puzzle always has exactly one correct solution, and you can always get there through deduction alone — no guessing required.

Understanding the Grid

Before you start solving, it helps to understand the structure:

• Rows: The 9 horizontal lines running left to right. Each must contain 1–9.
• Columns: The 9 vertical lines running top to bottom. Each must contain 1–9.
• Boxes: The nine 3×3 sections separated by thicker lines. Each must contain 1–9.
• Given numbers: The pre-filled numbers you cannot change. They are your starting clues.
• Empty cells: The cells you need to fill in.

Every cell in the grid belongs to exactly one row, one column, and one box. That intersection is what makes sudoku solvable — each constraint limits the candidates for every cell.

Your First Technique: Scanning

The most fundamental technique in sudoku is scanning. Pick a number — let's say 7 — and look across the entire grid to find where 7 already appears. Then use those positions to eliminate rows, columns, and boxes where a new 7 cannot go.

For example, if the top-left box is missing a 7, look at the rows and columns that run through it. If row 1 already has a 7, and row 2 already has a 7, then the 7 in the top-left box must go in row 3. Now check the columns in row 3 within that box — if one column already has a 7 elsewhere, only one cell remains. That's your 7.

Your Second Technique: Elimination

For each empty cell, ask: "What numbers are impossible here?" Look at the row, column, and box the cell belongs to. Every number that already appears in any of those three units cannot go in that cell.

If only one number is possible in a cell, that's called a naked single — fill it in immediately. This is the most common technique for beginners and will solve the majority of easy and medium puzzles on its own.

Your Third Technique: Cross-Hatching

Cross-hatching is scanning applied to boxes. Focus on one 3×3 box. For each missing number, draw imaginary lines across from its appearances in other rows and columns. Where those lines cross in your box, those cells are ruled out. If only one cell remains in the box for a given number, fill it in.

Cross-hatching and scanning together are all you need for Beginner and Easy puzzles. Practice these until they feel automatic before moving up to Medium.

How to Use Pencil Marks (Notes)

On Medium puzzles and above, single cells often have two or three candidates remaining after elimination. Instead of guessing, write all the possibilities lightly in the cell — these are called pencil marks or notes.

As you fill in other cells, go back and erase pencil marks that are no longer valid. Over time, pencil marks narrow down until a cell has only one candidate remaining — then you can fill it in with confidence.

On Sudokuzio, tap the Notes button before tapping a number to add pencil marks. Tap the same number again to remove it. Switch Notes off to place numbers normally.

Common Beginner Mistakes

• Guessing: If you're guessing, stop. Go back and look harder. Every sudoku has a logical path.
• Ignoring boxes: New players often focus on rows and columns but forget to check boxes. All three units matter equally.
• Not using pencil marks: On harder puzzles, trying to keep all candidates in your head leads to errors. Write them down.
• Skipping back to check: After placing a number, always scan the affected row, column, and box for new naked singles it might have created.
• Working in order: Don't solve left-to-right or top-to-bottom. Solve where you have the most information first.

Understanding Difficulty Levels

Sudoku difficulty is determined by how many cells are given at the start and which techniques are required to solve it:

• Beginner: 51+ given cells. Scanning and naked singles solve everything. Perfect for your first puzzles.
• Easy: 45 given cells. Scanning, cross-hatching, and basic elimination.
• Medium: 38 given cells. Pencil marks become useful. Hidden singles required.
• Hard: 32 given cells. Naked pairs and pointing pairs needed.
• Expert: 26 given cells. Advanced techniques including X-wing and swordfish.

Start on Beginner and don't rush to the next difficulty until Beginner feels genuinely easy — not just manageable, but easy. The jump between each level is significant.

Step-by-Step: Solving Your First Puzzle

1. Look at the given numbers. Find the rows, columns, and boxes with the most filled-in cells — those are your easiest starting points.
2. Scan for naked singles. For each empty cell, how many numbers are still possible? If only one, fill it in.
3. Cross-hatch each number. Go through 1–9 and use scanning to place numbers where they must go.
4. Add pencil marks. For any cell with 2–3 candidates, write them in.
5. Look for hidden singles. If a number appears as a pencil mark in only one cell of a row, column, or box — it goes there, even if that cell has other marks too.
6. Repeat. Every number you place opens up new deductions. Keep cycling through these steps until the puzzle is complete.

Tips for Getting Better Faster

• Play the daily puzzle every day. Consistency builds pattern recognition faster than anything else.
• After solving a puzzle, take 2 minutes to review any cells that gave you trouble. Understanding why the solution works cements the technique.
• Time yourself. Not to race, but to track improvement. Watching your time decrease over weeks is one of the best motivators.
• When you're stuck, don't guess — take a break and come back. Your brain often spots patterns it missed before.
• Move up difficulty levels gradually. Rushing to Expert before mastering Medium creates bad habits.