The rule of the square: can the king catch up?

Draw a square

A passed pawn runs for the last rank, and no other piece can stop it. Will the king catch up? Don't count moves. Picture a square instead: one side runs from the pawn up to the last rank, and the square is just as wide toward the king.

The square of the pawn: from the pawn up to the last rank, and just as far to the side. Black's king stands outside it. White to move wins with 1. c5, but only with that move.

If the king stands in the square, it catches up. If it stands outside, the pawn goes all the way. If the king is to move, it is enough that it can step into the square with its move.

The same position with Black to move: the king steps into the square with 1… Kg6 and catches the pawn. A draw.

After 1. c5 the square has shrunk to c5–f8. Black's king can't get into it in one move. The pawn goes all the way.

That's why 1. c5 wins: the square shrinks with every step the pawn takes, and Black's king can't get into it. A king move would have given Black time to step in.

The pawn on the second rank

A pawn still on its starting square may move two squares. So count the square as if the pawn already stood one step further up.

A pawn on the second rank may move two squares. So count the square from b3, not from b2. Here 1. b4 wins, while 1. b3 lets the king in and only draws.

When the rule isn't enough

The rule of the square counts only the king against the pawn. If something stands in the king's way, or the other king can come and help its pawn, the square doesn't tell the whole truth. And sometimes a king outside the square can make it in time after all, if it threatens something else at the same time. Richard Réti showed this in one of the most famous endgame studies there is.

Richard Réti's study from 1921. White to move and draw. The king on h8 looks hopelessly far from the h-pawn. Only 1. Kg7 saves White.

White's king stands far from the h-pawn, outside its square. But a king going diagonally moves forward just as fast as a king going straight, and on the way it can threaten two things at once: to catch the h-pawn and to help the c-pawn forward.

White to move. The king has to catch the h-pawn, but it stands outside the pawn's square.

1.
2.
3.
4.
5.
6.…

Open on the analysis board

The study was published in 1921 in the magazine Kagans Neueste Schachnachrichten. The idea is often called the Réti maneuver.

Practice against the computer

White to move. Draw the square in your head: will Black's king catch up if you make the right move? Then take the pawn all the way. The computer defends Black.

You are playing White. Make your first move.

You have White. Count the square, and take the pawn to the last rank. The computer defends Black.

Remember

The square shrinks with every step the pawn takes. A pawn move can be faster than a king move.
The double step counts. A pawn on the second rank counts as if it stood on the third.
The king is just as fast diagonally. A diagonal step takes the king just as far forward as a straight one.

When the king catches up but the pawn has its own king for support, the game is decided by the opposition and the key squares.

Frequently asked questions

What is the rule of the square?

A way to see whether a king can catch a passed pawn without help. Draw a square from the pawn up to the last rank, with sides just as long toward the king. If the king stands in the square, or can step into it with its move, it catches up.

How do you count with a pawn on the second rank?

The pawn may move two squares on its first move. So count the square as if the pawn already stood on the third rank.

When doesn't the rule of the square work?

When something stands in the king's way, or when the other king can come and help its pawn. The rule counts only the king against the pawn. Réti's study also shows that a king outside the square can make it in time, if it threatens something else at the same time.

Updated October 28, 2026