Tattoo Artist BooksHow to play sudoku: fill a 9x9 grid so that every row, every column and every 3x3 box contains the digits 1 to 9 exactly once. No adding or arithmetic is needed. Sudoku is a logic and elimination game, and the digits only work as symbols.
This guide covers the rules, simple sudoku strategies for your first puzzle, and the more advanced methods you can learn later. Learning sudoku techniques is far more enjoyable than guessing when you are stuck.
Sudoku rules
- The grid has 81 cells: 9 rows, 9 columns and nine 3x3 boxes.
- Some cells start filled in. These are the clues.
- Each row must contain 1-9 exactly once.
- Each column must contain 1-9 exactly once.
- Each 3x3 box must contain 1-9 exactly once.
- A well-made sudoku has exactly one solution, so you never need to guess.
A commonly told history: the puzzle appeared in the late 20th century in the US as "Number Place" and gained its name and popularity in Japan. If you need exact historical detail, check a reliable source.
First technique: naked single
If, after looking at a cell's row, column and box, only one digit can go there, write it in. This is the method you will use most. Example: if a box already has 1-8, the empty cell must be 9.
Second technique: hidden single
If a digit can go in only one cell of a row, column or box, write it there. Work by elimination: "Where can the 7 go in this box?" The 7s in neighboring rows and columns rule out most cells.
Pencil marks
On paper, write small candidate digits in empty cells. Phone apps call this notes mode. Notes are required for the advanced techniques and prevent wrong guesses.
Techniques by level
| Technique | What it does | Level |
|---|---|---|
| Naked single | Write a digit when a cell has only one candidate | Beginner |
| Hidden single | Write a digit when it has only one place in a row, column or box | Beginner |
| Naked pair | Two cells with the same two candidates remove those from other cells in the unit | Intermediate |
| Pointing pairs | If a digit in a box can only be in one row, remove it from the rest of that row | Intermediate |
| X-Wing | Candidates forming a rectangle across two rows and two columns | Advanced |
A step-by-step solving routine
- Scan the grid. Start with the rows, columns and boxes that have the most clues.
- Go digit by digit. For each of 1 to 9, scan the grid and ask where it can go.
- Go cell by cell. Look at the empty cells with the fewest candidates.
- Use pencil marks. When singles run out, write candidates and look for pairs.
- Do not guess. A guessed wrong digit can ruin the whole grid ten moves later.
Common mistakes
- Writing too fast: A hasty wrong digit causes a contradiction many moves later. Check row, column and box before writing.
- Skipping notes: Without them medium puzzles become much harder.
- Sticking to one area: When stuck, move elsewhere. A new digit placed somewhere else often unlocks the stuck region.
- Guessing: Instead of guessing, test a digit by elimination and prove the other one correct.
Levels and choosing a puzzle
Most sources label puzzles easy, medium, hard and expert, but labels vary by source. If a puzzle takes much longer than ten minutes and annoys you, step down a level. If you feel progress even after half an hour, the level is right. The most important thing at every level is learning the technique; speed comes with time.
Sudoku varieties
Besides the classic 9x9 there are 4x4 and 6x6 versions for children, diagonal variants and versions with letters. Once you know the classic grid they feel familiar, because the core rule stays the same: each symbol once per row, column and region.
Paper or phone?
Paper with a pencil and eraser makes notes and mistakes easy to handle, and a newspaper page is portable. Phones offer automatic notes, hints and error checking, but notifications can distract you. While learning, the hint feature helps; once you are comfortable, going back to paper can feel more satisfying.
What sudoku does for your mind
Sudoku is practice in patience, attention and logical elimination. Be careful with "improves your brain" claims. Evidence is mixed and solving sudoku does not always transfer to general intelligence. We go into detail in brain training games. For many people the real benefit is a calm, satisfying break. If you like it, also look at word games and puzzles.
Frequently asked questions
Where can I play sudoku for free?
Newspaper and magazine pages, printable grids and phone apps. When choosing an app, check ad density and offline support.
Do I need to be good at math?
No. You do not add or multiply. You could replace the digits with letters or shapes and the game would be the same.
Can a sudoku have no solution?
A correctly made one has exactly one. If you cannot finish, you have probably made a mistake earlier; check your notes.
Can children play sudoku?
4x4 and 6x6 or picture versions suit children. See brain games for kids for more child-friendly ideas.
At OdenaVerse we plan to build puzzle and logic games for adults. They are not out yet; our inbox is open if you have a game idea, and our overview of brain games for adults shows where sudoku fits.