Sudoku Rules — How to Play Sudoku
Sudoku takes two minutes to learn and a lifetime to master. Here is everything you need to play your first puzzle.
The Grid
Sudoku is played on a 9×9 grid of 81 cells. The grid is divided into nine rows, nine columns, and nine 3×3 boxes. Together, any row, column, or box is called a unit.
The Three Rules
- Each row must contain the digits 1–9 exactly once.
- Each column must contain the digits 1–9 exactly once.
- Each 3×3 box must contain the digits 1–9 exactly once.
The digits already printed on the grid are called givens (or clues) and cannot be changed. You fill in the empty cells until all three rules are satisfied everywhere.
A Worked Example
Look at the top-left 3×3 box. Suppose it already contains 1, 2, 3, 4, 5, 6, 7, and 8 — but no 9. Now check the only empty cell in that box: whichever row and column it sits in, the digit 9 is the only one that keeps the box complete, so 9 must go there. This "what is missing, and where can it fit?" reasoning is the heart of sudoku.
Key Terms
- Candidate: a digit that could still go in an empty cell without breaking any rule.
- Pencil mark / notes: small digits players write in a cell to track its candidates.
- Unique solution: a properly made puzzle has exactly one valid completion. All puzzles on Sudoku Whale are programmatically verified to have one.
- Bivalue cell: a cell with exactly two candidates — the fuel of most advanced techniques.
Frequently Asked Questions
Do I need to be good at math?
No. Sudoku uses digits but involves zero arithmetic — it is pure logic. The symbols could just as well be letters or colors.
Is guessing allowed?
You can, but you should never need to. A correctly constructed sudoku is solvable step by step with logic alone, and guessing usually creates contradictions that cost more time than it saves.
What is a good time for a puzzle?
Beginners often take 15–30 minutes on easy puzzles; experienced players finish easy grids in 4–8 minutes and hard grids in 15–40. Speed comes naturally with practice — accuracy first.
Where should I start solving?
Find the row, column, or box with the most givens and place missing digits there first. Then move to the digit that appears most often across the whole grid.
Once the rules click, learn how to solve faster in our sudoku strategies guide, or go practice on easy sudoku right away.