How to Play Sudoku: Rules and Techniques for Beginners
A sudoku grid looks intimidating, full of numbers, but its rule fits in one sentence and you can learn to solve it in minutes. There's no arithmetic involved: sudoku is a game of pure logic. This guide covers the rule, where to start a grid and the basic techniques so you never get stuck again. You can try it right now on our free online sudoku.
The only rule you need
A sudoku grid is a 9×9 square divided into nine 3×3 blocks. The goal is to fill every cell with the numbers 1 to 9 following a single rule: each number may appear only once per row, per column and per 3×3 block.
That's it. There's nothing to add up and nothing to guess: if you follow that rule, only one solution is possible. A good sudoku is always solved by logic, never by chance.
Where to start
The classic beginner's mistake is staring at a random empty cell. Instead, start by looking for the numbers that appear most often in the starting grid. If there are already lots of 7s, for example, find the blocks, rows and columns missing a 7: often there's only one possible cell.
This technique is called scanning: you take one number and check, block by block, where it can go. Since the same number can't repeat in a row or column, the options shrink fast and an "obvious" cell appears.
Candidates: the core technique
When scanning isn't enough, jot down in each empty cell the numbers still possible — these are the candidates. A cell with a single candidate gets filled in immediately.
Also watch for cases where, within a block, row or column, a number has only one cell it can go in: it goes there, even if that cell has several candidates. These two ideas — a cell with one candidate and a number with one spot — already solve most easy and medium grids.
Mistakes to avoid
- Guessing. If you have to try at random, there's still a deduction to find. A real sudoku never forces you to gamble.
- Not updating candidates. Every number you place removes possibilities elsewhere: remember to cross that candidate off its row, column and block.
- Tunnel vision. If you're stuck in one corner, switch numbers or blocks: the key is often at the other end of the grid.
How to improve
Getting better at sudoku is about practice, not talent. Start with easy grids until you solve them without hesitating, then move to medium, where scanning alone no longer cuts it. Once you're comfortable with candidates, take on hard sudoku: it requires chaining several deductions, and our tips for solving a hard sudoku will help you make the leap.
And if you're curious about where it came from, don't miss the history of sudoku.
Play now
The best way to learn is by playing. Open an easy grid, apply scanning and then candidates, and you'll see no cell is truly "impossible." And if you enjoy pure logic games, try our minesweeper too: same deduction reflexes, a different board. Have fun!