# Block

A square region containing 9 cells in a 3x3 formation. Boxes are usually surrounded by a thick border.

Together, the boxes form one of the 3 main divisions of the grid.

Each box is also a house, because it must contain digits 1 through 9.

Boxes are usually numbered from 1 to 9 in the following way:

```+---+---+---+
| 1 | 2 | 3 |
+---+---+---+
| 4 | 5 | 6 |
+---+---+---+
| 7 | 8 | 9 |
+---+---+---+
```

Without the boxes, Sudoku would only be a Latin Square. The presence of the box constraints has made it possible to develop several solving techniques that would not be possible in a Latin Square. The boxes have therefore greatly contributed to the popularity of Sudoku.

In discussions of Killer Sudoku the synonym "nonet" is most frequently used, largely to avoid confusion with the smaller boxes (cages) that are found in this type of puzzle.

## Related Terms

Aliases
block | nonet | region | subgrid
Belongs to
grid | floor | tower | division
Subtype of
house
Contains
9 cells | 6 intersections | 3 boxrows | 3 boxcols