The Square Rule
A quick visual method to determine whether a king can catch a passed pawn without needing to calculate every move.
Published 2026-02-01 | Last verified 2026-02-12
Professor Archer says: The square rule is the first endgame shortcut I teach every student. Without it, you have to count moves one by one to determine whether a king can catch a pawn, which is slow and error-prone. With the square rule, you can answer that question in a single glance. It is like learning to read instead of sounding out every letter. Once you know it, you cannot imagine not knowing it.
What Is the Square Rule?
The square rule is a visual shortcut for determining whether a king can catch a passed pawn. Instead of counting moves for both the king and the pawn, you draw an imaginary square from the pawn to the promotion square, with the sides extending to the side of the board.
The rule is simple: if the defending king can step inside this square on its next move, it will catch the pawn. If it cannot enter the square, the pawn will promote regardless of what the king does.
This works because the king and the pawn both move at the same speed (one square per move) in a straight line. The square represents all positions from which the king can intercept the pawn's path. If the king is outside the square, it is too far away to catch up.
The Square Rule in Practice
In this position, White has a passed pawn on a4. The square of the pawn extends from a4 to a8 (four squares to promote), and the side of the square extends four squares to the right (to e4 at the base, and e8 at the top).
If the black king is inside this imaginary a4-a8-e8-e4 square, it can catch the pawn. If it is outside, the pawn promotes. This visual check takes only a second and replaces tedious move-by-move calculation.
Can the black king catch the a-pawn? Draw the square to find out.
When the Square Rule Applies
The square rule works perfectly when the pawn has a clear path to promotion with no obstacles. It applies in king-and-pawn endgames when you need to quickly assess whether a pawn race will succeed.
There are important exceptions to keep in mind. The rule assumes the pawn advances one square at a time. On its first move, a pawn can advance two squares, which effectively extends the square by one row. Also, the rule does not account for other pieces that might block the pawn or support the king.
Despite these caveats, the square rule is an invaluable practical tool. In time pressure, it allows you to make accurate endgame decisions without lengthy calculation. It is one of the most useful shortcuts in chess.
Square Rule FAQ
Does the square rule work for all pawns?
Yes, the principle applies to any passed pawn. However, you must account for the pawn's first two-square advance option if it has not moved yet, and for any obstacles in the pawn's path.
What if there are other pieces on the board?
The square rule assumes a clear path. If other pieces can block the pawn or help the king, you need to calculate more carefully. The rule is most reliable in pure king-and-pawn positions.
Can I use the square rule for multiple pawns?
You can apply it to each pawn individually, but when multiple pawns are racing, the interactions become more complex. The square rule is best used as a quick check for single pawn situations.
Professor Archer says: Here is the rule in one sentence: if the defending king can step into the square of the pawn, it catches it. If not, the pawn promotes. The "square" is the imaginary box drawn from the pawn to the promotion square, with sides of equal length. Learn to visualise it instantly, and you will save countless minutes on the clock.
Quick Quiz
A white pawn is on b5, and the black king is on g7. The pawn needs 3 moves to promote. Can the king catch it?
- No, the king is outside the square and cannot catch the pawn (Correct) - Correct. The square of the b5 pawn extends from b5 to b8, with a width of 3 squares to the right (b5-e5 at the base). The king on g7 is outside this square and cannot enter it in time to stop the pawn.
- Yes, the king can reach the pawn in three moves - The king on g7 needs more than three moves to reach the b-file or the pawn's path. Drawing the square from b5 to b8 (3 squares wide) shows the king is too far away.
- It depends on who moves first - With the pawn already on b5 and the king on g7, the king is outside the square regardless of who moves first. The distance is simply too great.
- Yes, because the king can move diagonally - The square rule already accounts for diagonal king movement. Even moving diagonally, the king on g7 cannot enter the square of the b5 pawn in time.