Sudoku is a logic puzzle played on a 9×9 grid. The goal is simple: fill every row, every column, and every 3×3 box with the digits 1 through 9, each appearing exactly once. No maths required — only logical deduction. If you want to try your first puzzle right now, play free beginner sudoku at internetsudoku.net.

What Is Sudoku?

A sudoku puzzle starts with some cells already filled in — these are called givens or clues. Your task is to fill in every empty cell so that each row, each column, and each 3×3 box contains every digit from 1 to 9 exactly once. There is always exactly one correct solution, and you can always reach it through logical deduction alone — no guessing needed.

Sudoku has nothing to do with arithmetic. You never add, subtract, or multiply the numbers. The digits 1–9 are simply nine distinct symbols used for identification — you could use letters or colours instead and the puzzle would work identically. What matters is uniqueness, not calculation.

The Rules in 30 Seconds

• The grid is 9 columns wide and 9 rows tall — 81 cells in total.
• The grid is divided into nine 3×3 boxes (also called regions or blocks).
• Every row must contain the digits 1–9, each exactly once.
• Every column must contain the digits 1–9, each exactly once.
• Every 3×3 box must contain the digits 1–9, each exactly once.
• Pre-filled cells (givens) cannot be changed.
• There is exactly one valid solution for each puzzle.

How to Read the Grid

Think of the 9×9 grid in three overlapping layers:

1. Rows run left to right, numbered 1 (top) to 9 (bottom). Each row must contain 1–9.
2. Columns run top to bottom, numbered 1 (left) to 9 (right). Each column must also contain 1–9.
3. Boxes are the nine 3×3 sections. The grid has three rows of boxes — top, middle, bottom — and three columns of boxes — left, centre, right. Each box must also contain 1–9.

Every cell belongs to exactly one row, one column, and one box. That means each cell is constrained by three groups at once. When you place a digit, it immediately eliminates that digit as an option in 20 other cells — the 8 others in its row, the 8 in its column, and the 4 remaining in its box (accounting for overlaps). This is why sudoku is solvable through pure deduction.

Step-by-Step: Solving Your First Puzzle

1. Look for the most-filled rows, columns, and boxes first. A row with eight digits already filled in has only one possible answer for the remaining cell. Start with these — they are the easiest deductions on the board.
2. For each empty cell, check which digits are missing from its row, column, and box. The digit not yet present in all three groups is your answer for that cell (if only one such digit exists).
3. Fill in any cell where only one digit is possible. This is called a naked single — the most common move in beginner sudoku.
4. After filling in a cell, re-scan its row, column, and box. Your new digit creates new constraints that may immediately resolve another cell nearby.
5. Work systematically, not randomly. Go through the rows, columns, and boxes in order. A calm, methodical pass will solve most beginner puzzles without getting stuck.
6. Write down candidates if you get stuck. In each empty cell, write tiny pencil-mark notes for every digit still possible there. When a cell's list narrows to one, that is your answer.

Beginner Tips to Remember

• Never guess. A wrong digit creates contradictions that cascade across the grid. If you cannot see a logical move, look again — there is always one available.
• Work in the most-constrained areas first. Rows, columns, and boxes with many givens give you the most deductive power.
• Scan one digit at a time. Pick digit 5, for example, and scan every group on the board asking where 5 can still go. Often you will find a group where only one cell is available for 5.
• Take a break if you are stuck. A five-minute break resets your perspective and you will almost always spot the next move when you return.

How Long Does a Beginner Sudoku Take?

A beginner puzzle typically takes 10 to 20 minutes for a first-time player. With practice, the same puzzle takes under 10 minutes. Beginner puzzles are designed so every move follows from basic scanning — no advanced techniques are needed.

As you gain confidence, move to easy difficulty, then normal, then hard and extreme. Each level teaches new techniques — naked pairs, hidden singles, X-Wing — that carry over into faster, more elegant solves. See our complete sudoku strategies guide for the full technique progression.

Where to Play Sudoku Online

Internetsudoku.net offers five difficulty levels: Beginner, Easy, Normal, Hard, and Extreme. Each puzzle is generated fresh so you never replay the same grid. The daily challenge gives you one fixed puzzle per day, useful for tracking your improvement over time. All levels are free, no account required, and the game works on any device — phone, tablet, or desktop.

Frequently Asked Questions

How do you play sudoku for beginners?

Fill a 9×9 grid so that every row, column, and 3×3 box contains the digits 1 through 9 exactly once. Start with rows, columns, or boxes that already have many digits filled in — the cell with only one possible digit left is always your first move. No arithmetic is needed; only logical deduction.

Do you need to be good at maths to play sudoku?

No. Sudoku uses no arithmetic. The digits 1–9 are simply nine distinct symbols. You could replace them with letters A–I and the puzzle would work identically. The only skill required is logical thinking.

What is a naked single in sudoku?

A naked single is an empty cell where only one digit is possible after you eliminate all digits already present in its row, column, and 3×3 box. Finding naked singles is the core technique in beginner and easy sudoku.

How do you know when a sudoku solution is wrong?

A solution is wrong if any row, column, or 3×3 box contains a repeated digit. On internetsudoku.net you can reveal the correct numbers at any time to check your work, or use the automatic error highlighting to catch mistakes as you go.