The Rule of the Square

Overview

Can the king catch the pawn? In king-and-pawn races the answer costs the whole point, and the rule of the square answers it without any calculation. Grandmasters apply it in a second across the board; beginners count move by move — and still get it wrong on the far files.

Drawing the square

Draw a square whose side equals the pawn's remaining path: a pawn on e4 needs four ranks to promote, so the square is four by four, drawn toward the defending king. If the king stands inside that square (or can step inside while the pawn is still to move), it catches the pawn. If it is outside, no route exists — the pawn runs home unaided. In the diagram the king on c6 stands comfortably inside: it reaches the promotion path in time and the game is drawn.

Count the tempo

The rule has one refinement: whose turn is it. A pawn on e4 with the defender to move is caught by a king standing one square further away than with the attacker to move, because the pawn gains a tempo by pushing and shrinking its own square. Always redraw the square after the push — the tempo is the most common source of counting errors.

Practice positions

Play each position out against the engine from the exact spot on the board — unrated, you take the strong side.