How to Play Sudoku and Solve It Step by Step

How to play sudoku: fill the 9x9 grid so that every row, every column and every 3x3 box contains the digits 1 to 9 exactly once. The numbers already on the board are clues and cannot be changed. This page has a free interactive sudoku lesson that runs in your web browser. There is no sign-up and nothing to install, and puzzles are made on your own device, so nothing is uploaded.

The lesson covers the rules first, then 12 solving techniques, then a complete puzzle you can step through. Work through it in order if you are new, or jump to the technique you need.

How to use the sudoku lesson

1. Part 1, The rules: Start with the 4x4 practice board. Each row, column and 2x2 box must hold the numbers 1 to 4 once. If you repeat a number, it turns red straight away, so you can see the mistake at once.
2. Part 2, Techniques: Pick one of the 12 techniques. The board shows a real position where that technique is the next move.
3. Press Show step. Yellow cells are the pattern, blue cells are the row, column or box involved, red circles are candidates to remove, and green is the digit to place.
4. Press Apply step to make the move. Then press Next technique to move on, or Reset to start again.
5. Part 3, A whole puzzle: Choose the easy, medium or hard example.
6. Press Next step to move through the solve one step at a time. The solver always uses the easiest technique that makes progress, and it keeps a list of steps with a count for each technique.
7. Press Back one step to undo a step, or Solve all to finish the puzzle at once.

For a paper copy, use the Print cheat sheet option. It prints on one page, Letter or A4, with all 12 techniques, a one-sentence description of each and a diagram of a real position.

How do you play sudoku?

You play sudoku by writing digits 1 to 9 into the empty cells of a 9x9 grid. Each row, column and 3x3 box must end up with every digit exactly once. You can only place a digit where it does not repeat one already in its row, column or box.

What are the sudoku rules for beginners?

The rules are short. Every row, column and 3x3 box contains the digits 1 to 9 exactly once. The given digits cannot be changed, and a proper sudoku has exactly one solution. Because of that, every correct answer is the same grid.

How to start a sudoku puzzle?

Start by looking for a hidden single. Pick a digit, then look at one box, row or column and find the only cell where that digit can still go. Place it, then look for naked singles: a cell where only one digit is still possible.

How to solve sudoku step by step?

Work through the puzzle in this order:

1. Place every hidden single and naked single you can see.
2. When singles run out, write candidates (small pencil marks) in each empty cell. These are the digits that could still go there.
3. Look for patterns in the candidates, such as locked candidates, pairs and triples.
4. Fill in the new single that each step reveals, then repeat.

How to solve sudoku when stuck?

When you are stuck, write all candidates first. Then look for locked candidates: a digit confined to one row or column inside a box, or to one box inside a row or column. After that, check pairs and triples, and then the X-Wing and Y-Wing patterns.

What is an X-Wing?

An X-Wing is a pattern across two rows. In each of the two rows, a digit can go in only two cells, and those cells sit in the same two columns. The digit can then be removed from the rest of those two columns. The same idea works with columns and rows swapped.

What is an XYZ-Wing?

An XYZ-Wing uses a pivot cell with three candidates, X, Y and Z. It sees two other cells, one holding candidates XZ and one holding YZ. Digit Z can be removed from any cell that sees all three of these cells.

How do sudoku puzzles work?

A sudoku puzzle gives you some digits as clues, and each clue narrows down what the empty cells can be. A solver moves forward by finding cells that have only one possible digit, or patterns that rule out digits elsewhere. Guessing is never needed in a proper easy, medium or hard puzzle on this site. Expert puzzles are the ones the 12 techniques cannot finish.

Frequently asked questions

How do you play sudoku with numbers only?

Yes. Sudoku uses only the digits 1 to 9, so you need no letters or symbols. Write the digits into the grid and check each row, column and box as you go.

How to solve a sudoku fast?

Scan for hidden singles and naked singles first, because they often give placements without any pencil marks. Only write candidates when those run out.

How do you solve any sudoku without guessing?

With logic alone: proper easy, medium and hard puzzles on this site can be solved with logic alone. If you find yourself guessing, look again for a missed single or a candidate pattern.

What does a repeated number mean in the practice board?

A repeated number in a row, column or 2x2 box turns red straight away. That means the placement breaks the rules, so remove it and try a different digit.

Why does a proper sudoku have only one solution?

A proper sudoku is designed so the clues leave exactly one way to complete the grid. This is why every correct solution matches.

Can I see the solution step by step?

Yes. In Part 3, press Next step to move through the solve, or Back one step to review an earlier move.

Related tools

• Sudoku solver: use it when you want the answer to a puzzle you are stuck on.
• Easy sudoku: use it to practise with puzzles that need only the simplest techniques.
• 4x4 sudoku: use it for a smaller board that teaches the rules quickly.
• Printable sudoku: use it when you want puzzles on paper.
• Hard sudoku: use it once you are comfortable with pairs, X-Wings and other patterns.
• Killer sudoku: use it for a sudoku variant that adds cage sums to the classic rules.
• Daily sudoku: use it to keep up a regular solving habit with a new puzzle each day.