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How to Play Sudoku: A Complete Beginner's Guide

Sudoku is one of the world's most popular logic puzzles - and it requires absolutely no math. Whether you have never touched a Sudoku grid before or you want a clear refresher, this guide walks you through everything you need to know to start solving puzzles with confidence.

What Is Sudoku?

Sudoku is a number-placement puzzle played on a 9×9 grid divided into nine 3×3 boxes (also called regions or blocks). The goal is simple: fill every empty cell with a digit from 1 to 9 so that each row, each column, and each 3×3 box contains every digit exactly once.

Howard Garns created the puzzle in 1979, first published as "Number Place" in Dell Pencil Puzzles & Word Games. It was renamed "Sudoku" by Nikoli Co. in Japan in 1984 - from the Japanese phrase "sūji wa dokushin ni kagiru," meaning "the digits must remain single." Today it appears in over 2,000 newspapers across 80+ countries.

Sudoku uses numbers, but it is purely a logic puzzle. You could replace the digits with letters, colors, or symbols and it would work the same way. No arithmetic is involved - only deduction and elimination.

Understanding the Sudoku Grid

A standard Sudoku grid has 81 cells arranged in 9 rows and 9 columns. The grid is further divided into nine 3×3 boxes, separated by thicker lines.

↔ Row - A horizontal line of 9 cells running left to right across the grid. There are 9 rows total.

Row 1 highlighted - 9 cells running left to right

↕ Column - A vertical line of 9 cells running top to bottom. There are 9 columns total.

Column 5 highlighted - 9 cells running top to bottom

▣ Box (Region) - A 3×3 group of 9 cells outlined by thicker borders. There are 9 boxes total.

Box 5 highlighted - a 3×3 region in the center of the grid

When a puzzle starts, some cells are already filled with digits. These are called "givens" or "clues." The number of givens determines the puzzle's difficulty - easy puzzles have more givens (36-45), while evil puzzles have very few (17-22).

The Three Rules of Sudoku

Every Sudoku puzzle follows exactly three rules. If you remember these, you know everything you need to get started:

Rule 1: Each row must contain the digits 1 through 9, with no repeats

Look at any horizontal row in the grid. When the puzzle is complete, that row will contain each of the digits 1, 2, 3, 4, 5, 6, 7, 8, and 9 exactly once.

Rule 2: Each column must contain the digits 1 through 9, with no repeats

The same rule applies vertically. Every column from top to bottom must have all nine digits with no duplicates.

Rule 3: Each 3×3 box must contain the digits 1 through 9, with no repeats

Each of the nine 3×3 boxes (outlined by thicker borders) must also contain all nine digits exactly once. This is the constraint that makes Sudoku uniquely challenging.

A completed Sudoku - row 1 (blue), column 9 (green), and box 5 (amber) each contain 1–9 exactly once

How to Solve a Sudoku Puzzle: Step by Step

Follow these steps to solve your first Sudoku puzzle. We will start with the simplest techniques that work on easy and medium puzzles.

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Step 1: Scan the Grid

Before placing any digit, take a moment to scan the entire grid. Look for rows, columns, or boxes that are nearly complete - these are the easiest places to find a solution. If a row has 8 of 9 digits filled in, the missing digit is the answer for the empty cell.

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Step 2: Use Cross-Hatching

Pick a digit (say, 1) and scan each 3×3 box to see where that digit can go. Look at the rows and columns that pass through the box - if a row or column already contains that digit, it eliminates cells in the box. When only one cell remains, that is where the digit goes.

Cross-hatching: each highlighted 9 blocks its entire row and column. In the bottom-right box, only one cell remains for a 9 (green)
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Step 3: Apply the Last Remaining Cell Technique

If a row, column, or box has only one empty cell left, the missing digit is the only possibility. Fill it in immediately. This often triggers a chain reaction - filling one cell may leave another group with only one remaining.

Last remaining cell: box 1 has eight digits filled - the only one missing is 5 (green)
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Step 4: Use Pencil Marks (Notes)

For cells where multiple digits are possible, write small candidate numbers (pencil marks) in the cell. On Sudoku91, toggle Notes mode to do this. As you fill in digits elsewhere, come back and eliminate candidates that are no longer possible.

Pencil marks show which digits could still go in each cell. R2C2 (blue) has three candidates: 2, 4, and 7
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Step 5: Look for Naked Singles

A naked single is a cell where only one candidate remains after elimination. Check your pencil marks - when a cell has been reduced to a single candidate, that digit is the answer. Fill it in and update surrounding pencil marks.

Column 5 already contains 1–4 and 6–9. Only 5 is missing - the green cell must be 5
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Step 6: Find Hidden Singles

A hidden single occurs when a digit can only go in one cell within a row, column, or box - even if that cell has multiple candidates. For example, if the digit 7 can only go in one cell within a particular row, it must go there regardless of what other candidates that cell has.

Hidden single: the blue 5s block columns 5 and 8. In row 5, only the green cell can hold a 5, even though it also has 8 and 9 as candidates
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Step 7: Repeat and Solve

Continue scanning, cross-hatching, and checking for singles until the entire grid is filled. For easy and medium puzzles, these techniques are usually sufficient to reach the solution.

Common Mistakes Beginners Make

Guessing instead of deducing

Every Sudoku puzzle with a unique solution can be solved through pure logic. If you feel like guessing, you have likely missed an elimination somewhere. Step back and re-scan the grid.

Forgetting to update pencil marks

When you place a digit, remember to remove that digit from the pencil marks in the same row, column, and box. Stale pencil marks lead to confusion and errors.

Focusing on one area too long

If you are stuck in one section of the grid, move to a different area. Progress elsewhere often unlocks cells you were stuck on earlier.

Common Misconceptions

"You need math skills to play Sudoku"

False. Sudoku involves zero arithmetic. You never add, subtract, multiply, or divide. The digits are just symbols - the puzzle is purely about logic and pattern recognition.

"There can be multiple solutions"

A properly constructed Sudoku puzzle has exactly one unique solution. If a puzzle has multiple solutions, it is considered invalid. All puzzles on Sudoku91 are computer-validated to ensure a single solution.

"You sometimes have to guess"

Never. Every valid Sudoku puzzle can be solved through logic alone. If you feel like guessing, it means there is a technique you have not applied yet - not that the puzzle requires luck.

"The more givens, the easier the puzzle"

Usually true, but not always. The placement of givens matters as much as the quantity. A puzzle with 30 well-placed givens can be easier than one with 28 poorly placed ones. That said, as a general rule, more givens means fewer logical steps to solve.

"Sudoku was invented in Japan"

Partially true. The modern Sudoku format was first published as "Number Place" by Howard Garns in Dell Magazines (USA) in 1979. It was later introduced to Japan by Nikoli in 1984, where it gained the name "Sudoku" and became a global phenomenon.

Tips for Sudoku Beginners

Ready to Play?

Now that you know the rules and basic techniques, put your knowledge into practice. Start with an easy puzzle and work your way up as your skills improve.

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Sudoku Solver

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Sudoku Strategies

Ready to level up? Learn scanning, naked pairs, X-Wing, and more techniques from beginner to advanced.

FAQ

Do you need to be good at math to play Sudoku?
No. Sudoku uses numbers as symbols, but no arithmetic is involved. It is purely a logic and deduction puzzle. You could replace the digits with letters or shapes and the puzzle would work identically.
How long does it take to solve a Sudoku puzzle?
It depends on the difficulty and your experience. Beginners typically take 15-25 minutes on an easy puzzle, while experienced solvers finish in under 5 minutes. Hard and expert puzzles can take 30-60 minutes or more. A 2019 University of Exeter study found that regular puzzle solvers maintain sharper cognitive function, so the time you spend is well invested.
What if I get stuck on a Sudoku puzzle?
Take a break and come back with fresh eyes. Re-scan the entire grid systematically. Check for hidden singles you may have missed. On Sudoku91, your progress is auto-saved, so you can return anytime.
Is there always only one solution to a Sudoku puzzle?
Yes. A properly constructed Sudoku puzzle has exactly one unique solution. In 2012, mathematicians Gary McGuire, Bastian Tugemann, and Gilles Civario proved that 17 is the minimum number of givens needed for a unique solution. All puzzles on Sudoku91 are validated to ensure a single solution reachable through logic alone.