A cell is a single square in the Sudoku grid. Each of the 81 cells holds exactly one digit from 1 to 9.
A cell is a single square within the Sudoku grid that holds exactly one digit from 1 through 9 when the puzzle is complete. A standard 9x9 Sudoku grid contains 81 cells, arranged in 9 rows and 9 columns, and grouped into 9 boxes of 3x3 cells each.
Each cell is uniquely identified by its position in the grid, typically described by its row number (top to bottom) and column number (left to right). For example, the cell in the third row and fifth column is often referred to as R3C5. This notation is commonly used in strategy discussions and puzzle communities.
To learn the complete rules governing cells and the grid, visit our Sudoku rules page.
Every cell in Sudoku is governed by three constraints simultaneously. The digit placed in a cell must not appear anywhere else in the same row, the same column, or the same 3x3 box. These three overlapping constraints are what make Sudoku a challenging logic puzzle.
Each cell "sees" exactly 20 other cells: 8 in its row, 8 in its column, and 4 additional cells in its box that are not already counted by the row and column. Any digit that appears in one of these 20 peer cells is eliminated as a candidate for the cell in question.
At the start of a puzzle, cells are either filled (givens or clues) or empty (to be solved). Given cells are placed by the puzzle designer and provide the starting information from which you deduce everything else. They cannot be changed during solving.
An unsolved cell has multiple candidates - digits that could potentially go in that cell. As you apply solving techniques, candidates are eliminated until only one remains, at which point the cell is solved. A completed puzzle has all 81 cells solved with no constraint violations.
Ready to start solving? Check out our how to play guide for a step-by-step introduction. Explore more terms in the Sudoku glossary.
A standard 9x9 Sudoku puzzle contains exactly 81 cells, arranged in 9 rows and 9 columns. Each cell holds exactly one digit from 1 through 9 when the puzzle is completed.
Every cell in a standard Sudoku puzzle is subject to three constraints: its row, its column, and its box. The digit placed in a cell must be unique within all three of these groups. This means each cell is influenced by up to 20 other cells.
A given cell (also called a clue) is pre-filled by the puzzle designer and cannot be changed. An empty cell is one that the solver must fill in. The number of given cells determines much of the puzzle's difficulty.
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