Learn · Notation

How to read a sudoku grid

Two minutes here will make every hint, forum post and solving guide readable.

Cells

RnCm means row n, column m. Rows run top to bottom, columns left to right. R1C1 is the top-left cell; R9C9 is the bottom-right.

A value is written R4C8=6. An elimination is written R4C8≠6.

Boxes

The nine 3×3 boxes are numbered B1–B9 in reading order: B1 top-left, B2 top-middle, B3 top-right, B4 middle-left, and so on. A cell belongs to one row, one column and one box — those three are its units.

Candidates

The digits that could legally go in an empty cell are its candidates (also called pencil marks or notes). Written as a set: {2,6,9}. A cell with exactly two candidates is a bivalue cell — those are the cells wings are built from.

Peers

Two cells that share any unit are peers. Each cell has 20 peers: 8 in its row, 8 in its column, 4 more in its box. Peers are why one placement can eliminate twenty candidates at once.

Reading our hints

A hint on this site always has the same three parts:

1. the technique name — so you can look it up and practise it,
2. the reason on your board — which unit, which cells, which digit,
3. an optional action — “place 6 at R4C8” or “3 candidates can be removed”.

If you only ever click the action, you get a digit. If you read the reason, you get the technique. The second one is the point.