In one line

A sudoku grid has 81 cells in nine rows, nine columns and nine 3×3 boxes. Some cells start with a digit. You fill in the rest so that every row, column and box holds each digit from 1 to 9 exactly once.

Before thisNothing. This is the first page on the path, and it assumes you have never solved a sudoku.

the house we are working incells the pattern ownsShading marks the rows, columns and boxes a step is talking about. The marked cell is the one being named.

Rows, columns and boxes

Rows run across and columns run down, nine of each. Rows are numbered from the top, columns from the left.

Thick lines cut the grid into nine boxes, counted the way you read a page: box one top left, box three top right, box nine bottom right.

Rows, columns and boxes follow one rule, so they share a name: a house. Every cell sits in three houses.

A row, a column and a box.

Naming a cell

A cell is named row first, then column. The marked cell is row six, column three, and every article here names cells this way. Written short, it is r6c3, or R6C3 in the game's solver panel.

The order matters. Row three, column six is another cell, up in box two.

Row six meets column three.

Givens and empty cells

The starting digits are the givens, and they never change. This grid has 36 givens and 45 empty cells to fill. Box one starts with six givens. Box five, in the middle, has two.

Box one and box five.

The one rule

Each digit goes once in every house. So a digit already in a cell's row, column or box cannot go in that cell.

Take row six, column three. Its row holds a 3, a 4 and a 7. Its column adds a 1 and a 9, and its box adds a 5. That leaves 2, 6 and 8.

One of them belongs here, and these houses cannot yet say which. Each ruled out a digit the other two missed, so read all three.

The three houses of row six, column three.

What comes next

The digits a cell can still take are its candidates. Writing them small in the cell is called pencil marks, the next stop. When a cell's houses leave one digit, the cell is solved. That is the last possible number.

One question

What is the marked cell called, and which box is it in?

Count rows down from the top and columns across from the left. Boxes are counted the way you read a page.

Recap

Look for: A cell's name, row first: row six, column three, or r6c3.
Scope: A cell's three houses: its row, its column and its box.
Result: Any digit already in one of them is ruled out for the cell.
If it fails: If a name seems to point at the wrong cell, read it again row first. Then track each cell's candidates with pencil marks.

Reading the Grid