How to Read Sudoku Notation

Rows, columns, cells and boxes

Rows are numbered one to nine from top to bottom, and columns are numbered one to nine from left to right. A single cell is named by its row and column together, which pins it down exactly on the grid. The common shorthand writes r for row and c for column, so r4c7 means the cell in the fourth row and the seventh column. Some writers flip the order and put the column first, and a few use plain coordinates, but the meaning is always the same one cell. The nine three by three blocks, meanwhile, are called boxes, and they are usually numbered one to nine in reading order: box one is the top left, box three is the top right, box five is the centre, and box nine is the bottom right. So when a guide says a digit is locked in box five, it means the digit is confined to that central block. Learning the box numbers well enough to place them at a glance saves you from counting blocks every time a technique refers to one, and together with the rc notation it lets any move be described without a diagram at all.

Units, peers and candidates

• A unit is any single row, column or box, the three kinds of group in which every symbol must appear exactly once.
• Two cells are peers if they share at least one unit, because one of them taking a value rules that value out for the other.
• A candidate is a value that could still legally go in a cell, the small pencil marks you keep as notes while solving.
• A given, or clue, is a symbol printed at the start that never changes, while the rest of the cells are yours to fill in.

Strong links and conjugate pairs

Two more terms show up constantly in advanced guides, and they are worth locking in early. A conjugate pair is a unit in which a particular digit has only two candidate cells left, which means exactly one of those two cells is that digit and the other is not. A strong link is the relationship between them: if one cell is not the digit, the other one must be. These sound like small definitions, but an enormous amount of higher Sudoku is built directly on them. Techniques from the Skyscraper to Simple Coloring are, at heart, nothing more than chains of strong links traced through the grid, so once the phrase conjugate pair feels natural, a whole shelf of strategy articles suddenly becomes readable rather than cryptic. It is the single vocabulary step that separates a beginner guide from an intermediate one.

A worked sentence, and move shorthand

Put the vocabulary to work on a real instruction: remove five from r2c3 and r2c8 because of an X-Wing on columns three and eight. Decoded, that says look at the digit five, notice that it forms a rectangle across columns three and eight, and because of that pattern you may erase five as a candidate from two specific cells in row two. Once the shorthand is familiar, a sentence like that is actually faster to read than its plain-English translation, and it points you at the exact squares to change. Guides compress the moves themselves too. You will see r5c5 equals 7, meaning that cell is solved as seven, and r5c5 with a strikethrough on 7, meaning seven is removed there as a candidate. A list such as r1c2, r1c5 and r1c9 simply groups several cells that share a single reason. None of this is meant to show off; it is a shared shorthand that lets a writer describe a precise move in a handful of characters and lets you replay it faithfully on your own grid.

Putting it together

Learn the small handful of terms above and the whole strategy world opens up, because every technique article, forum post and solver log leans on exactly the same shorthand. There is no competing standard to trip over, just minor variations in ordering, so the effort you spend now pays off across everything you read later. Best of all, the notation does not care in the slightest whether your board shows digits or shapes. In Shapedoku, r4c7 still names one particular cell, a conjugate pair is still just two places a single shape could go, and box five is still the middle block. Keep this page handy for a week, refer back to it whenever a guide throws an unfamiliar abbreviation at you, and the shorthand will soon feel like a first language rather than a code you have to stop and decrypt every time. That small investment quietly upgrades every strategy article you will ever read afterwards.