Chess rules
The Chess Board: Files, Ranks, Diagonals & Squares
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A chess board has 64 squares in an 8×8 grid of alternating light and dark colours. The vertical columns are files (lettered a–h), the horizontal rows are ranks (numbered 1–8), and every square has a unique name combining its file and rank — like e4.
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Files, ranks and diagonals
The board is mapped from White’s point of view. Files are the eight columns running away from you, labelled a to h from left to right. Ranks are the eight rows, numbered 1 (nearest White) to 8 (nearest Black). Diagonals are the slanted lines of one colour — the longest runs from a1 to h8 and from h1 to a8. Bishops travel along diagonals; rooks travel along files and ranks.
How squares are named
Each square is named by its file letter then its rank number, always file first. So the square in White’s near-left corner is a1; the far-right corner is h8. The four central squares — d4, d5, e4 and e5 — matter in the opening because pieces and pawns there can influence both wings and restrict the opponent.
Light squares and dark squares
The 64 squares split into 32 light and 32 dark, and the colours alternate so that no two squares of the same colour touch edge-to-edge. A bishop remains on one colour for the entire game, so exchanging that bishop can change who controls a group of squares. Strategists often call a square weak when a pawn can no longer challenge an enemy piece there; pieces may still defend it, but that defence can become a lasting duty.