Classic Sudoku: Fill the Grid with 1 to 9

About Classic Sudoku

The classic sudoku is the timeless number puzzle, now in your browser and with no need for a pencil or eraser. In front of you is a 9×9 grid divided into nine 3×3 boxes, with some cells already revealed. Your mission is to fill in the rest so that every row, every column and every box contains every number from 1 to 9 without repeating any. Luck and speed don't count here: what counts is reasoning calmly and justifying every number you place. If you like this kind of challenge, you'll find plenty more in our section of online sudoku.

Before you start you can choose the difficulty level, so it works for someone playing their first sudoku as well as for someone looking for grids with very few clues. It's a great mental workout for any age and fits just as well into a free moment as into a classroom activity.

How do you play Classic Sudoku?

The rule is simple, although mastering it takes time. Each number can appear only once in its row, once in its column and once in its 3×3 box.

1. Choose the difficulty level you prefer.
2. Select an empty cell on the board.
3. Enter the number that, by your reasoning, belongs there.
4. Repeat until you've filled all 81 cells without breaking any rule.

Classic Sudoku controls

PC

• Mouse click: select a cell and choose a number

Mobile and tablet

• Screen tap: select a cell and choose a number

What do you learn in Classic Sudoku?

• Logical reasoning and deduction by elimination.
• Sustained concentration and patience not to rush.
• Working memory, by keeping several constraints in mind at once.
• Computational thinking: following fixed rules and testing hypotheses step by step.

Recommended for ages 8 and up; the easy levels are ideal for getting started with family or in class.

Tips to play better: Classic Sudoku

• Start with the rows, columns or boxes that already have the most numbers: there are fewer options and it's easier to deduce.
• Go through the board number by number: look for where each 1 can go, then each 2, and so on.
• If a cell allows only one possible value, place it; if it allows two, leave it for later.
• Avoid guessing: a number placed at random can block the whole board several steps later.

Classic Sudoku FAQ

Do you need to know math to play classic sudoku?

No calculations are needed. The numbers work as symbols: what matters is the logic to avoid repeating them in the same row, column or box.

What level of classic sudoku should I choose if I'm starting?

Start with the easiest level, which shows more initial clues. When you solve it without hesitating, raise the difficulty little by little.

Can you play classic sudoku on your phone?

Yes. It works in the browser on PC, tablet and mobile, and on touch screens you just tap the cells.

Additional information: Classic Sudoku

Game type: Sudoku / number logic
Recommended age: Ages 8 and up
Technology: HTML5
Platform: Web browser (PC, tablet and mobile)

Enjoyed Classic Sudoku? Also try Queens game, Suguru Online or Daily Sudoku. Find more Online Sudoku and hundreds of games you can play in your browser on LudoRex.