Square of the pawn

The square of the pawn is an imaginary area used to compare a pawn's race toward promotion with the opposing king's route. Promotion happens when the pawn reaches the last rank and becomes a queen, rook, bishop, or knight.

To picture it, use the distance between the pawn and its promotion square as one side of the square, then extend the same distance toward the side where the opposing king stands. If the pawn still has a legal initial two-square move, imagine it one square farther forward before drawing the shape, because those two squares cost only one move. The boundary counts as part of the square.

Building the square from b2

8

7

6

5

4

3

2

a1

b

c

d

e

f

g

h

The white pawn is on b2 and still has its legal two-square first move.

The double move changes the count

The white pawn is on b2 and still has its legal two-square first move. To construct the area, use b3 as the reference, count five moves to b8, and extend the same width to the g-file. The black king on g4 stands on that lateral boundary.

1. The white pawn is on b2 and still has its legal two-square first move.

The square is the geometric area . The rule of the square is the test that uses it to decide whether the king arrives in time. The idea is cleanest when the pawn is running unaided and no other piece blocks, checks, or changes the move count.