Sudoku Notation

How sudoku players talk about cells, candidates, and patterns. Useful if you're reading strategy posts on forums or watching solving videos.

Cell references. r1c1, r5c5

Sudoku players reference cells as r<row>c<col>. r1c1 is the top-left cell. r9c9 is the bottom-right. r5c5 is the centre. Rows are numbered top-to-bottom, columns left-to-right. Some books use 1–9 for both; others write R1C1. The standard is the same.

Pencil marks (candidates)

Small digits written in an empty cell to record which values are still possible. There are two common styles: positional(the digit goes where it would visually go inside a 3×3 mini-grid within the cell) and list (just comma-separated digits). Positional is faster to scan visually.

Cage notation (killer sudoku)

Killer sudoku cages show the sum total in the top-left corner of the cage. Cells in a cage are connected by dotted borders. See killer sudoku for the full rules.

Common shorthand

r1c5=3. "place 3 in row 1, column 5"
r1c5≠3. "eliminate 3 from r1c5"
b4. "box 4" (boxes numbered 1–9 left-to-right, top-to-bottom)
{1, 4}. a candidate set; cell can only be 1 or 4