The Square of the Pawn
A simple visual rule to determine whether a king can catch a passed pawn before it promotes.
Published 2026-02-01 | Last verified 2026-02-12
Professor Archer says: I love teaching the Square of the Pawn because it is one of those rare chess concepts that is both profound and immediately useful. The first time I showed it to a student, she said, "You mean I can figure out an entire race between a king and a pawn just by drawing a square in my mind?" Yes. That is exactly what it means. It is one of the most satisfying shortcuts in chess, and it works every single time.
The Rule Explained
In pawn endgames, one of the most common questions is: "Can my king catch that pawn, or will it promote?" Calculating the race move by move is possible, but there is a much faster method: the Square of the Pawn.
Here is how it works. Imagine the pawn is about to advance. Count the number of squares between the pawn and its promotion square (the eighth rank for a white pawn, the first rank for a black pawn). Now draw an imaginary square on the board, with one side running from the pawn to the promotion square and the other side extending sideways by the same distance.
If the enemy king is inside this square, or can enter it on its next move, the king will catch the pawn. If the king is outside the square and cannot enter it, the pawn will promote. It is that simple.
The reason this works is geometry. The king can move diagonally, which means it covers distance both vertically and horizontally at the same rate. If the king is within the same number of moves of the promotion square as the pawn, it will arrive in time. The square is a visual shorthand for this diagonal equivalence. Once you learn to draw the square in your mind, you can assess pawn races instantly, without calculating a single move.
Applying the Rule
Let us apply the rule to the position shown. White has a pawn on b2, and Black has a king on d5. White is considering pushing the pawn.
If White plays b4, the pawn is now on b4 and needs four moves to reach b8 (b4-b5-b6-b7-b8). We draw the square: from b4, count four squares up to b8, then extend four squares to the right. The square runs from b4 to b8 to f8 to f4 and back to b4.
Is the black king on d5 inside this square? We check: d5 is within the boundaries of b4-f4-f8-b8. Yes, the king is inside the square. Therefore, the king can catch the pawn.
But what if the pawn were on b5 instead? The square would be b5-b8-e8-e5. Is d5 inside? Yes, just barely. The king can still catch it. Now try b6: the square is b6-b8-d8-d6. The king on d5 is outside this square, so if the pawn reaches b6 with Black to move, Black still catches it (entering the square at d6). But if it is White's turn and the pawn advances from b6 to b7, the square shrinks to b7-b8-c8-c7 — and the king is too far away.
This kind of precise visualisation is what makes the square rule so powerful. Instead of calculating five or six individual moves, you simply draw a shape and look.
The pawn is on b4. The Square of the Pawn stretches from b4 to f8. The black king on d5 is inside — it catches the pawn.
Important Caveats
The Square of the Pawn is a reliable rule, but it has a few caveats that you must keep in mind to avoid errors.
First, the rule only works when the pawn's path is clear. If there are other pawns or pieces blocking the pawn's advance, the square calculation does not account for the delays. You need a clear run to the promotion square for the rule to apply directly.
Second, remember to adjust the square after the pawn's first move. From its starting position on the second rank, a pawn can advance two squares in one move. This means the "effective" starting point for the square is one square further than you might think. When the pawn is still on the second rank, draw the square as if the pawn is on the third rank (because it will reach the third rank in one move).
Third, the rule does not account for blocking pieces or defensive tricks. If the enemy king's path into the square is blocked by your own pieces, the king may not actually be able to enter the square despite being geometrically inside it. Similarly, if the king's path leads through check or other tactical complications, the rule needs adjustment.
Despite these caveats, the Square of the Pawn works cleanly in the vast majority of practical positions. It is the first tool I reach for whenever I see a pawn race developing, and it saves enormous calculation time.
Questions About the Square of the Pawn
Does the Square of the Pawn work for both colours?
Yes. For a white pawn, the square extends from the pawn's position toward the eighth rank. For a black pawn, it extends toward the first rank. The direction changes, but the principle is identical. Draw the square toward the promotion rank and check whether the opposing king is inside.
What if the pawn is on its starting square?
A pawn on its starting square can advance two squares on its first move. To account for this, draw the square as if the pawn were already one square further advanced. This slight adjustment ensures the rule remains accurate for the two-square first move.
Can I use this rule in time trouble?
Absolutely, and that is one of its greatest strengths. In time trouble, calculating a pawn race move by move is error-prone and time-consuming. The Square of the Pawn gives you an instant answer. With practice, you can draw the square in your mind in under two seconds.
Professor Archer says: Practice this technique with random positions until it becomes automatic. Set up a pawn and a king on any squares, and before you calculate any moves, draw the square in your mind and predict the result. Then play it out. Within an hour of practice, you will own this tool for life. It is one of the best investments of study time you can make.
Quick Quiz
White has a pawn on a5 and Black's king is on f5. It is White's turn. Can the pawn promote?
- Yes, because the black king is outside the square of the pawn (Correct) - Correct. The pawn on a5 needs three moves to reach a8 (a5-a6-a7-a8). The square extends from a5 to d5 to d8 to a8. The king on f5 is outside this square and cannot enter it in time after White plays a6.
- No, because the king can always catch a pawn from the fifth rank - The rank of the king does not automatically determine whether it can catch the pawn. What matters is whether the king is inside the square. Here, the king on f5 is too far to the right of the a-pawn's square.
- No, because a-pawns can never promote without king support - A-pawns can absolutely promote without king support if the enemy king is far enough away. The Square of the Pawn rule determines whether the king can intervene, regardless of which file the pawn is on.
- It depends on whether the pawn can advance two squares - The pawn on a5 has already passed its starting square, so it can only move one square at a time. The two-square first move only applies from the second rank.