Rules and first strategy
How to play Sudoku step by step
The goal is to fill every cell without repeating any number. It sounds simple — and the rule is — but every number you place reshapes the possibilities for many other cells.
The goal of the game
A Sudoku starts with some cells already filled in, called clues or givens. Your job is to fill the rest so that each allowed number appears exactly once in every row, every column, and every region marked by a thicker border.
The numbers don't stand for quantities: you could swap them for colours, letters, or symbols and the puzzle would work the same. That's why playing Sudoku takes no arithmetic — it takes recognising patterns and ruling out possibilities.
Once per row
Each row must contain every number of the chosen format, with no repeats.
Once per column
The same rule applies vertically: no number may appear twice in a column.
Once per region
Each bordered block must contain every number exactly once.
Sudoku 6×6 and Sudoku 9×9
At LookThis.One Games you can pick between two sizes. The logic is exactly the same; what changes is how many cells and numbers you juggle at once.
Sudoku 6×6
Great for starting- Uses the numbers 1 to 6.
- Has 6 rows and 6 columns.
- Its regions are 2×3 cells.
- Lets you learn the rules with less to track at once.
Sudoku 9×9
The classic format- Uses the numbers 1 to 9.
- Has 9 rows and 9 columns.
- Its regions are 3×3 cells.
- Offers a much wider range of techniques and difficulty.
First technique: find the only possible spot
A good way to start is to scan rows, columns, and regions for a missing number. Then rule out the cells where that number can't go because it already appears in the matching row or column.
An example of elimination
In the third row, the numbers 3, 5 and 6 are missing. The highlighted cell can't be 3 or 5 because both already appear in its column. By elimination, the only possible value is 6.
The answer is deduced, not guessed.A simple method for your first games
- Look at the fullest regions.
Blocks with more givens usually offer the first deductions, because fewer options remain.
- Look for numbers that appear often.
If a 4 already sits in two regions of the same band, you can often pin down where it goes in the third.
- Note your candidates.
When a cell allows two or three numbers, keep them as possibilities. As you go, some will be ruled out.
- Alternate between rows, columns, and regions.
Don't fixate on one area — a deduction elsewhere can unlock it.
- Check before moving on.
Make sure the new number doesn't repeat. Catching a mistake early saves rebuilding half the game.
Two ideas that speed up learning
Naked single
Happens when a cell allows only one possible number. Even if its row still has several empty spaces, the constraints of its column and region can leave a single answer.
Hidden single
Happens when a number can go in only one cell within a row, column, or region. That cell may have several candidates noted, but for that particular number it's the only place available.
What to do when you get stuck
Take a break and scan the board in a different order. Check the regions first, then the rows, and finally the columns. You can also focus on a single number — say, find every possible spot for the 7 — instead of looking at every cell at once.
If you're playing online, use the hint feature as a learning tool: before you accept it, try to explain why that cell holds that value. Turning an answer into a reason is what strengthens your method.
A journey across continents
The history of Sudoku
Its name is Japanese, its modern form appeared in an American magazine, and its worldwide spread got a decisive push from a British newspaper.
Before Sudoku: Latin squares
Sudoku belongs to a family of combinatorial problems related to Latin squares: grids in which each symbol appears exactly once per row and per column. The mathematician Leonhard Euler studied these structures in the 18th century, though Sudoku adds an essential constraint: it also divides the grid into inner regions.
That doesn't mean Euler invented modern Sudoku. It's more accurate to see Latin squares as a mathematical ancestor that helps explain why the game's rules are so elegant.
Euler studies Latin squares
The idea of not repeating symbols across rows and columns becomes a formal object of mathematical study.
“Number Place” appears
The modern form of the game is published in the American magazine Dell Pencil Puzzles and Word Games and is generally credited to the constructor Howard Garns.
Nikoli brings it to Japan
The Japanese publisher adapts the puzzle, runs it for its readers, and ends up shortening its name to “Sudoku”.
International explosion
The Times begins running it in November 2004. Other papers follow, and in 2006 the first World Sudoku Championship is held in Lucca, Italy.
From “Number Place” to “Sudoku”
Nikoli says it found the puzzle in an American magazine and introduced it to Japan in 1984. Its first Japanese title was a much longer phrase, Sūji wa dokushin ni kagiru, hinting that the numbers had to stay “single” — appearing only once. As it was unwieldy, it was trimmed to Su-doku: “number” and “single”.
The leap to newspapers worldwide
New Zealander Wayne Gould came across the game on a visit to Japan and spent years building a program that could generate new boards. In 2004 he convinced The Times of London to publish it. The combination was perfect for print: short rules, little space, and an experience that didn't depend on language or cultural knowledge.
The spread was dizzying. Other papers added their own versions, whole books appeared, and Sudoku went from a pastime known mainly in Japan to an international phenomenon.
Stories inside the grid
Sudoku anecdotes and fun facts
Behind its minimalist rules is a story with a forged mock-up, gigantic mathematical results, and an idea that works even without numbers.
The “forgery” that helped convince The Times
When Wayne Gould turned up unannounced at the offices of The Times, he needed to show quickly that Sudoku could sit alongside the paper's puzzles. As he later told it, he bought a copy of the paper, cut and rearranged parts of a page, and slotted in one of his Sudokus to create a mock-up that looked authentic.
The mock-up made his case for him: no one had to imagine how the game would look in the paper, because it already seemed to belong. The pitch worked, and the paper ran its first Sudoku on 12 November 2004.
One of Sudoku's strengths is that its instructions fit in a few lines, while the depth of its problems can grow enormously.
Paraphrased from the puzzle's editorial and mathematical history.
The minimum number of clues
A classic Sudoku with a unique solution can't have only 16 clues. An exhaustive computer search proved the minimum possible is 17.
Complete boards
That's roughly how many valid complete 9×9 grids exist before grouping rotations, reflections, and other symmetries.
Calculations required
You never add or multiply. The digits are labels; the difficulty comes from the constraints and how they interact.
First world championship
The first official world competition was held in Lucca, Italy, and won by Jana Tylová of the Czech Republic.
A Japanese puzzle that wasn't born in Japan?
That apparent contradiction is part of its charm. The modern format was published in the United States; Japan gave it the name the world now knows and helped refine its presentation; then a New Zealander helped it reach the British press at scale. Sudoku is the result of an international chain of ideas.
The numbers could be flowers, animals, or planets
Because there's no arithmetic, any set of nine distinct symbols could replace the numbers 1 to 9. Digits are used because they're compact, universal, and easy to tell apart — not because the game needs their numeric value.
Fewer clues doesn't always mean harder
A board with few givens can be easy if the first deductions are obvious. Another with more clues can demand complex techniques because of how they're arranged. Difficulty depends more on the logical path required than on how many cells come pre-filled.
A small problem with an enormous scale
The classic board has just 81 cells, but its combinatorial possibilities are gigantic. This tension between a simple interface and an immense solution space is why Sudoku fascinates players, mathematicians, and computer scientists alike.