Rows, columns and boxes are also known collectively as houses. Each of the 27 houses in the grid must be filled with the numbers 1 to 9 once with no repeats!
The standard 9x9 sudoku grid is divided up into 81 cells in which a single number from 1 to 9 is placed. Each cell belongs to three houses: one row, one column and one box.
The standard 9x9 sudoku grid is divided up into 9 rows. Within each row there are 9 cells in which the numbers from 1 to 9 must appear once each.
The standard 9x9 sudoku grid is divided up into 9 columns. Within each column there are 9 cells in which the numbers from 1 to 9 must appear once each.
The standard 9x9 sudoku grid is divided up into 9 boxes. Each box (or block) is 3x3 cells in size (9 cells in total) and is laid out with a central 3x3 box and eight 3x3 boxes around it, usually marked with thicker or darker borders. Each box must contain the numbers from 1 to 9, with each number appearing only once.
Now the grid has been completed and you'll see each of the numbers from 1 to 9 appear once, and only once, in every row, column and box, with the number 8 in the centre of the grid common to all three highlighted houses.
It is helpful to reference a particular cell, row, column or box when describing techniques. There are two main methods used.
The first is by referring to a row or column number, starting from the top left. For example, row 2 column 5 is the central cell in box 2. This can be shortened to r2c5. Box 2 can be shorted to b2. You can also refer to multiple cells in shorthand notation such as r2c258 (row 2, columns 2,5 & 8), which are the central cells in b123 (boxes 1,2 & 3).
Or you can use a coordinate system by labelling the rows by numbers 1 - 9 and the columns A - I. The same central cell in box 2 would be E2.
Play online sudoku now or check out our 300 Sudoku Puzzles: Easy to Extreme book! Or start off with 150 Easy Sudoku Puzzles.
