What Is Sudoku?

Sudoku is a number-placement puzzle played on a 9×9 grid divided into nine 3×3 boxes. The goal is simple: fill every empty cell with a digit from 1 to 9 so that each row, each column, and each 3×3 box contains the digits 1 through 9 exactly once. No math is required—only logic and patience.

Many puzzles start with some cells already filled. Those given numbers are fixed; your job is to deduce the rest using the rules above. There is only one correct solution per puzzle, and every valid Sudoku can be solved by logic alone, without guessing.

The Rules in Practice

Before placing a number, check three things: the row, the column, and the 3×3 box that cell belongs to. If you put a 5 in a cell, that 5 cannot appear anywhere else in that row, column, or box. Beginners often focus on one number at a time—for example, finding all the places 1 can go—then move to the next number.

• Each row of 9 cells must contain 1–9 with no repeats.
• Each column of 9 cells must contain 1–9 with no repeats.
• Each 3×3 box must contain 1–9 with no repeats.

Your First Puzzle

Start with an easy puzzle that has more given numbers (often 35 or more). Look for rows, columns, or boxes that are almost full; they usually have only one or two empty cells, so you can fill them quickly. From there, new possibilities open up. Take your time and double-check before writing a number down.

Once you are comfortable with the rules, try our Sudoku tips and strategies to solve faster. To choose the right challenge, read about Sudoku difficulty levels. For ongoing improvement, see how to get better at Sudoku.