Classic Sudokus in size 9x9 contain 81 cells that can have a value between 1 and 9. Some of these cells are predetermined and therefore visible. Others must be discovered by the player through logical considerations.

Even though numbers have become the most common variant, they can also be replaced by letters, symbols or similar. The only requirement is that they are distinguishable alternatives.

For easier navigation, a Sudoku is divided into rows that are labeled with numbers and columns that are assigned letters. This makes it easy to find cells in solution aids, for example.

In the example, column G and row 4 are highlighted. This marks the cell with the coordinates G4.

On a Sudoku board, the numbers in the cells are either given or have to be revealed by the players.

One Sudoku contains classic Sudoku puzzles in sizes 4x4, 9x9 and 16x16.

Note: 16x16 Sudokus are not available on devices with small screens (for example Example mobile phones).

In every Sudoku, each number can only appear once in all boxes, columns and rows. In the example of a 9x9 Sudoku, this means that the numbers 1 to 9 can only be used once in the 3x3 boxes, the rows and columns, each with nine number fields (the cells). If a number has already been given or has been revealed by the player, it can be excluded from all other cells in the column, row or box.

In this example, we solve a 4x4 Sudoku puzzle together. All strategies discussed can easily be transferred to other sizes and Sudoku variants. If you have never solved a Sudoku before, the 4x4 variant is a good starting point into the exciting world of this logic puzzle.

In the example, four of 16 numbers are given. The remaining hidden numbers can be found through elimination and other strategies.

By the newly found 2 at B3 we can furthermore enter the 2 by the same technique at A2 and C1. With this, all twos are already uncovered.

By a similar technique we can find the last possibility of all ones. If we follow the only currently revealed 1 at C1, we find the last possible position for the 1 at C4 in the bottom right box. With this 1, we can go up column 3 and find only one possible cell for the 1 in the upper right box at D1. And with this we can also uncover for the box on the left the position of the 1 at B2.

To finally solve the Sudoku, we can now determine that a 4 is missing for the upper left box and a 3 for the lower right box. By entering these two numbers, the Sudoku is completely revealed and thus solved.