The Rule of the Square
The Rule of the Square is the simplest and most useful endgame tool: it tells you instantly whether a king can catch a passed pawn, without calculating a single move. Draw a mental square from the pawn to the promotion square. If the king is inside the square (or can enter it on the next move), it catches the pawn. If not, the pawn promotes.
How it works
Draw an imaginary square from the pawn's current position to the promotion square. The square extends equally to the side. If the opposing king is inside this square (or can step into it on the next move), the king catches the pawn. If the king is outside the square, the pawn promotes.
Important exceptions
- The rule doesn't account for obstacles, pawns or pieces blocking the king's path.
- It doesn't apply to knights, they zigzag.
- Remember the pawn gets two squares on its first move, adjust the square accordingly from the starting rank.
Training
Quiz yourself with random K vs P positions. Can the king catch the pawn? Use the rule of the square to answer instantly, then verify against the computer.