Anatomy of a Sudoku Grid
The parts of a Sudoku grid explained: cells, rows, columns, boxes, bands, stacks and the units that drive every deduction.
Solving Sudoku is easier once you can name the parts of the grid. The board is built from 81 cells arranged in 9 rows and 9 columns, grouped into nine 3×3 boxes. Rows, columns and boxes are collectively called "units" — the groups that must each contain 1–9 exactly once.
A few wider groupings are useful too: three boxes in a horizontal row form a "band", and three boxes stacked vertically form a "stack". Knowing this vocabulary makes every technique easier to describe and follow.
The building blocks
Every deduction in Sudoku is about a unit — a row, a column or a box. When you place or eliminate a digit, you are reasoning about which cells of a unit can still hold it.
- Cell — one of the 81 squares; holds a single digit.
- Row — a horizontal line of 9 cells.
- Column — a vertical line of 9 cells.
- Box — a 3×3 block of 9 cells (also called a region).
- Unit — any row, column or box (each must hold 1–9 once).
- Band — three boxes side by side; stack — three boxes top to bottom.
How the units overlap
Each cell belongs to exactly three units: one row, one column and one box. The cells that share a unit with a given cell are its "peers" — 20 of them on a 9×9 grid. A digit placed in a cell is immediately forbidden in all 20 of its peers, and that overlap is the engine behind every solving technique.
Try it yourself
Tap a cell, then a number, to practise.
Frequently asked questions
- How many cells does a 9×9 Sudoku have?
- 81 — nine rows of nine. They are grouped into nine 3×3 boxes, and each cell sits in one row, one column and one box.
- What is a "unit" in Sudoku?
- A unit is any group that must contain the digits 1–9 exactly once: a row, a column, or a box. Most techniques are stated in terms of units.
Related reading
Practice online
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