Rows and columns are two of the three constraint groups in Sudoku. Each must contain the digits 1 through 9 exactly once.
A row is a horizontal line of nine cells running from left to right across the Sudoku grid. A column is a vertical line of nine cells running from top to bottom. A standard 9x9 Sudoku puzzle contains 9 rows and 9 columns, together creating 81 cells.
Each row must contain the digits 1 through 9 exactly once, and each column must independently contain the digits 1 through 9 exactly once. These two constraints, combined with the box constraint, form the complete rule set of standard Sudoku. For the full rules, see our Sudoku rules page.
Rows are conventionally numbered 1 through 9 from top to bottom, and columns are numbered 1 through 9 from left to right. Cells are identified by their row-column position, such as R3C5 (row 3, column 5). This notation is widely used in strategy discussions and guides.
Row and column constraints work by limiting which digits can appear in each cell. If a row already contains the digit 5, then no other cell in that row can contain 5. The same applies to columns. Every cell is constrained by both its row and its column simultaneously, plus its box.
This overlapping constraint system is what makes Sudoku solvable through logic. A digit that is valid from a row perspective might be invalid from a column or box perspective. The solver must consider all three constraints together to determine the correct placement for each digit.
Many advanced strategies are specifically based on row and column patterns. The X-Wing technique, for example, uses the alignment of candidates across two rows and two columns to make eliminations. When a candidate appears in exactly two cells in each of two rows, and those cells share the same two columns, the candidate can be removed from all other cells in those columns.
Row-column interactions with boxes also create opportunities. Pointing pairs and box-line reduction exploit situations where a candidate within a box is confined to a single row or column, allowing eliminations in the rest of that line outside the box.
Explore more Sudoku terms in the complete glossary.
A standard Sudoku puzzle has 9 rows and 9 columns, creating a grid of 81 cells. Each row runs horizontally from left to right, and each column runs vertically from top to bottom.
Each row must contain every digit from 1 through 9 exactly once, and each column must also contain every digit from 1 through 9 exactly once. This is the same constraint that applies to boxes, making three types of constraint groups in total.
Rows are numbered 1 through 9 from top to bottom. Columns are numbered 1 through 9 from left to right. A cell is typically identified by its row and column number, such as R3C5 for the cell in row 3, column 5.
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