How to Play Sudoku

Sudoku is a logic puzzle played on a 9×9 grid. Your goal is to fill every empty cell with a number from 1 to 9 so that each number appears exactly once in every row, every column, and every 3×3 box.

You don't need to be good at maths to play Sudoku. The numbers are simply symbols: solving the puzzle is about observation, elimination, and logical deduction.

If you've never played before, this guide will take you from understanding the grid to making your first moves and solving a Sudoku puzzle step by step.

How Sudoku works

A standard Sudoku puzzle contains 81 cells arranged in a 9×9 grid.

The grid is divided in three different ways:

• 9 rows, running horizontally.
• 9 columns, running vertically.
• 9 boxes, each containing 3×3 cells.

Every row, column, and box must eventually contain all the numbers from 1 to 9 exactly once.

When a puzzle begins, some cells already contain numbers. These starting numbers are usually called clues or givens. You cannot change them.

The remaining cells are empty, and your job is to determine which number belongs in each one.

Rows, columns, boxes, and cells

Every empty cell belongs to three groups at the same time: one row, one column, and one 3×3 box.

That relationship is the key to solving Sudoku.

Before placing a number in a cell, you need to check all three groups. If a number already appears in that cell's row, column, or box, it cannot be placed there.

This simple rule creates all of the logic behind the puzzle.

What is the goal of Sudoku?

The goal is to complete the entire grid without breaking any of Sudoku's three fundamental rules:

1. Every row must contain the numbers 1 through 9 without repetition.
2. Every column must contain the numbers 1 through 9 without repetition.
3. Every 3×3 box must contain the numbers 1 through 9 without repetition.

A completed grid therefore contains every number many times overall, but never twice within the same row, column, or box.

For a more detailed explanation of what makes a move valid, see our Sudoku Rules guide.

How to play Sudoku step by step

You don't need to understand advanced techniques to solve your first Sudoku. Beginner puzzles can often be completed by repeatedly looking for missing numbers and eliminating impossible positions.

1. Look for areas with lots of clues

When you first open a Sudoku, don't try to work through the grid from the top-left corner to the bottom-right.

Instead, scan the whole puzzle.

Look for rows, columns, or 3×3 boxes that already contain many numbers. The more clues an area contains, the fewer possibilities remain for its empty cells.

2. Find which numbers are missing

When an area contains several empty cells, work out which numbers have not appeared yet.

You can't immediately know which empty cell contains which number, so now you need more information.

That's where columns and boxes become useful.

3. Check the row, column, and box

Take one of those empty cells and check the other groups it belongs to.

Suppose that cell could contain either 3 or 5 based on its row.

If its column already contains a 3, then 3 is impossible in that cell.

The only remaining possibility is 5.

You can place 5 with confidence.

This process of removing impossible candidates is called elimination, and it is one of the foundations of Sudoku solving.

4. Only place numbers you can justify

A good Sudoku puzzle is designed to be solved logically.

If you're unsure whether a cell should contain 2 or 7, don't simply choose one and hope it works.

Leave the cell unresolved and look somewhere else.

Why can this number go here, and why can't the other numbers?

If you can answer that question, you're making a deduction rather than a guess.

5. Repeat the process

Every number you place changes the puzzle.

A row that previously had three empty cells may now have two. A box that offered several possibilities may suddenly have only one. A number that could appear in two positions may now fit in only one.

That's why Sudoku is solved iteratively:

scan → eliminate → place → scan again.

Don't worry if one part of the grid seems impossible to solve. Move somewhere else and return to it later.

A simple Sudoku example

Imagine a 3×3 box containing:

1  2  3
4  _  6
7  8  9

The box already contains 1, 2, 3, 4, 6, 7, 8, and 9.

The only missing number is 5, so the centre cell must be 5.

Now imagine that the box has two empty cells instead:

1  2  3
4  _  6
7  _  9

The missing numbers are 5 and 8.

Looking at the box alone isn't enough to decide where each one belongs.

But if the column containing the first empty cell already has an 8 elsewhere, that cell cannot contain 8. It must therefore be 5, leaving 8 for the other cell.

That's Sudoku in its most basic form: use the information you already have to eliminate what isn't possible.

What are pencil marks in Sudoku?

Sometimes you won't be able to determine a cell immediately.

Instead, you may know that it could contain one of several numbers.

For example, after checking its row, column, and box, you might determine that a cell can only contain:

These possible values are called candidates.

Pencil marks — often called notes in digital Sudoku games — let you record those candidates without committing to a final answer.

As you solve more of the puzzle, candidates can be removed.

Notes become increasingly useful as puzzles get harder because they make the remaining possibilities visible instead of forcing you to remember them.

Beginner Sudoku techniques

The basic process of scanning and elimination can be developed into several recognised Sudoku techniques.

You don't need to master all of them before playing, but understanding a few beginner techniques will make solving much easier.

These techniques are enough to solve many beginner puzzles. When you're ready to go further, our Sudoku Strategies guide explores solving techniques in more detail.

Common beginner mistakes

Does Sudoku require maths?

No.

Sudoku uses numbers, but it isn't an arithmetic puzzle. You never need to add, subtract, multiply, or divide anything to solve a standard Sudoku.

The digits 1 through 9 simply represent nine different symbols. In theory, you could replace them with nine letters, colours, or shapes and use exactly the same solving logic.

What Sudoku tests is your ability to recognise constraints, eliminate possibilities, and make logical deductions.

What difficulty should a beginner choose?

If you're new to Sudoku, start with an Easy puzzle.

Easy puzzles tend to offer more straightforward deductions and give you more opportunities to practise scanning, elimination, naked singles, and hidden singles.

Once those techniques start to feel natural, move to Medium.

Harder Sudoku puzzles aren't necessarily difficult simply because they contain fewer starting clues. Difficulty also depends on the types and combinations of logical techniques required to reach the solution.

What should you do when you get stuck?

Getting stuck is a normal part of solving Sudoku.

Before assuming that you need a more advanced technique, try rescanning the puzzle.

• Rows with only a few empty cells.
• Columns with only a few empty cells.
• Nearly completed 3×3 boxes.
• Cells with very few candidates.
• Numbers that haven't been placed often in a particular area.

You can also switch perspective. Instead of asking what belongs in this cell?, choose a number and ask where can this number go?

If basic scanning no longer reveals anything, that's a good time to explore more advanced Sudoku strategies.

Frequently asked questions