The Pawn's Square - A Chess Endgame Basic

In chess, you are sometimes confronted with a situation in which the only pieces left on the board are a pawn and two kings (King and Pawn vs. King). To achieve victory, the player with the king and pawn must move his pawn to the other side of the board, thus promoting the pawn to a queen. The goal of the player with a king is to capture/prevent the pawn from reaching the back rank.

If you're the player with the pawn, you're going to start moving your pawn forward, one space at a time, eventually hoping for the promotion. But can you make it without the king intercepting you? At this point, you would probably start working the moves out in your head: "Well, if I move to c4, he will move to g3; then I go onto c5, and then he goes onto f4," but this can prove to be fatal. First, if you rush it, then you may miscalculate and try to run for it when you should have brought your king over and tried to gain opposition. Second, it's the endgame, so every second counts. There is a quick and error-free solution, however. It's called the Pawn's square, and it will immediately tell you if you can make it to the other side.

It's pretty simple, really. Starting from the spot where the pawn currently resides, draw an imaginary line which stays on the current diagonal and goes to the other end of the board. With that, you now have the dimensions of the square. Here is an example:

+---+++++++++++++++++++++---+---+
|   +   |   |   |   | / +   |   | 8
+---+---+---+---+---+---+---+---+
|   +   |   |   | / |   +   |   | 7 
+---+---+---+---+---+---+---+---+
|   +   |   | / |   |   +   |   | 6
+---+---+---+---+---+---+---+---+
|   +   | / |   |   |   +   |   | 5
+---+---+---+---+---+---+---+---+
|   +WP |   |   |   |   +BK |   | 4
+---+++++++++++++++++++++---+---+
|   |   |   |   |   |   |   |   | 3
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |WK |   |   | 2
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   | 1
+---+---+---+---+---+---+---+---+
  A   B   C   D   E   F   G   H

- The Pawn's square is outlined in bold "+"
- The diagonal for which you find the dimensions of the square is seen with the bold "/"

The square goes from b4 to b8 to g8 to g4. So now you know what the square is and how to draw one, but now what? Well, the rule of the square is:

If the king can get inside the square, he will catch the pawn; if he can't, the pawn will promote safely.

So, if it was black's turn, the king would be in the square, and the pawn wouldn't be able to promote safely. Though, if it was white's turn, the pawn would be home free. Pretty cool, eh? I should probably note that the square isn't strictly limited to the King and Pawn vs. King endgame. It's perfectly possible for this technique to be valid if there are other pieces on the board. You just have to watch for pieces which block the king's path, thus making the square invalid. For example:

+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   | 8
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   | 7 
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |BP |   |   | 6
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   | 5
+---+---+---+---+---+---+---+---+
|   |   |   |BK |   |   |   |WP | 4
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   | 3
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   | 2
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |WK |   |   | 1
+---+---+---+---+---+---+---+---+
  A   B   C   D   E   F   G   H

Technically, since black is in the square (h4-h8-d8-d4), he should be able to catch the pawn. However, since the black pawn blocks the king's direct path to the pawn, the pawn will reach the back rank.

1. h5 Ke5 - I'm going to get this pawn.
2. h6 Ke6 - Ah shit, I'm out of the square.
3. h7 Kf7 - One more!
4. h8-Q - White is promoted to queen.

+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |WQ | 8
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |BK |   |   | 7 
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |BP |   |   | 6
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   | 5
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   | 4
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   | 3
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   | 2
+---+---+---+---+---+---+---+---+
|   |   |   |   |   |WK |   |   | 1
+---+---+---+---+---+---+---+---+
  A   B   C   D   E   F   G   H

So, Remember:

- To get the square, start at the pawn's position and follow it diagonally to the back rank. Those are your dimensions.
- As long as the opposing king isn't in the square, you're home free.
- If there are other pieces on the board besides a pawn and two kings, the square may not be totally accurate.