Sooner or later every puzzle conversation needs to point at one square. "The star in the third row, near the right" works until the board is 10×10 and three people are reading it on their phones. So solvers settle on a naming system, and then discover that the person replying uses a different one.
There are four systems in common use. Each makes sense somewhere, and two of them look alike but count in opposite directions. Here is what each one means, where it comes from, and which to use when you share a solve.
The Grid We'll Use
Every example below refers to this 5×5 grid. The star sits in the second row from the top, fourth column from the left.
In each system below, that star is:
- R1C1 style: R2C4
- Zero-based R0C0 style: R1C3
- Spreadsheet A1 style: D2
- Plain words: row 2, column 4
R1C1: Row First, Then Column
R1C1 names a cell by its row number and then its column number, counting from 1 at the top-left corner. R2C4 is row 2, column 4. It is the standard in Sudoku circles: forum write-ups, solving videos and most published walkthroughs use it, so many grid-puzzle players already read it without thinking.
It has two strengths. It is unambiguous, because the letters say which number is the row and which is the column. And it scales: a 10×10 or 14×14 board needs no new symbols, because R10C12 reads the same way as R2C4.
Solvers also shorten it for groups of cells. R3C4-6 means row 3, columns 4 to 6. R1-3C2 means rows 1 to 3 of column 2. Sudoku players go further and write R1C25 for "row 1, columns 2 and 5", but that shortcut breaks on boards with ten or more columns, where C25 could mean column 25 or columns 2 and 5. On a 10×10 board, write the columns out or use a comma: R1C2,5.
The only cost is length. R2C4 is four characters where D2 is two, which matters a little when you are typing a long chain of deductions on a phone.
R0C0: The Programmer's Version
Some people count from zero, so the top-left cell is R0C0 and our star is R1C3. If you write code this feels natural, because arrays in most programming languages start at index 0.
In a shared discussion it causes trouble. R1C3 is a perfectly good cell in the ordinary R1C1 system, just a different one, and nothing in the name tells a reader which counting the writer meant. One person counting from zero in a thread full of people counting from one produces confident, wrong replies. Use it in your own notes if you like, but switch to counting from 1 when you post.
A1: The Spreadsheet System
The spreadsheet system uses letters for columns and numbers for rows, with A1 at the top-left. Our star is D2. Anyone who has used Excel or Google Sheets, or played Battleship, already knows it.
It is the most compact system, and that is its real advantage. A deduction like "D2 rules out C3, D3 and E3" is quick to write and quick to read.
It has three drawbacks:
- Columns have to be counted. Most people know D is the fourth column instantly. Fewer know that H is the eighth or J is the tenth without counting on their fingers.
- The order is reversed. A1 names the column first and the row second; R1C1 names the row first. D2 and R2C4 are the same cell, but if you switch between systems it is easy to read D2 as "row 4, column 2".
- Some letters look like numbers. In some fonts a capital I looks like a 1 and an O like a 0, which can make column I or O hard to read on a 10×10 board.
Chess Notation: Same Look, Opposite Direction
Chess also names squares with a letter and a number, like e4. The difference is that chess counts rows from the bottom, from White's side of the board, so a1 is the bottom-left square. In a spreadsheet, A1 is the top-left.
Because the two look identical, this is the easiest mistake in the whole subject: a chess player reads "B2" and looks near the bottom of the grid, while everyone else looks near the top. Puzzle grids almost always count from the top, so leave chess notation for chess.
Plain Words
"Row 2, column 4" needs no explanation at all. It is longer, but nobody misreads it, which makes it the right choice when you are explaining a puzzle to someone new, or writing for a general audience. Our own step-by-step solutions use it for exactly that reason: every step says "row 7, column 6" rather than R7C6, so a first-time solver can follow along.
Notice that it lists the row first, the same order as R1C1. Anyone who reads plain words can switch to R1C1 just by shortening them.
What About Regions?
Cells have coordinates. Regions, the outlined or coloured shapes in puzzles like Star Battle, do not, and there is no standard way to name them. Solvers use whatever is clearest for the board in front of them:
- By colour, when the regions are filled: "the yellow region".
- By position or shape: "the L-shaped region in the top-right".
- By a cell inside it: "the region containing R1C1". This is the most precise, and it works on boards where several regions share a colour or a shape.
Which Should You Use?
If you are sharing a solve with other puzzle players, use R1C1, counting from 1 at the top-left. It is the most widely recognised system among grid-puzzle solvers, it cannot confuse rows with columns, it works on boards of any size, and it reads in the same order as plain words.
If a group already uses another system consistently, use theirs. Consistency matters more than which system wins. Whatever you choose, it helps to say so once at the start, for example "using R1C1, top-left is R1C1", so nobody has to guess whether you count from zero or from the bottom.
And if you are explaining a puzzle to someone who has never seen these systems, skip the notation entirely and write "row 2, column 4". It takes a few more characters, and nobody has to learn anything first.