Take the square the pawn stands on and its promotion square. The distance between them is the side of the square. Complete the square towards the enemy king: if the king can step into it on its move, it catches the pawn. If it cannot, the pawn runs through.
With White to move the pawn gets through: 1.h5, and the square shrinks faster than the king can enter it. With Black to move, 1...Kd5 puts the king on the edge of the square and the pawn is caught. The same picture on the board gives a different result - it all depends on whose move it is, and that is the whole point of the method.
It is easiest to count by files: from the pawn to the promotion square is five squares, counting the pawn's own, so you also count five files towards the king - as far as the d-file. Anything further left is outside the square.
If the king is already inside the square, there is nothing more to calculate: it walks diagonally towards the pawn and picks it off on the promotion square or earlier.
The calculation confirms it: the position is drawn with White to move and with Black to move. The king goes f6, g7 and meets the pawn on h8. The white king on a1 is seven moves away from the pawn - it is far too late to help.
The practical lesson for the defender: in an ending that looks lost, check the square first and only then think about resigning. A king that has entered the square stops the pawn with no technique at all.
From its starting square a pawn can move two squares at once, and that breaks the naive count. The square has to be drawn not from the pawn itself but from the third rank - as if the double step had already been made.
With White to move the pawn gets through: 1.h4! - and the king can no longer catch it. If you count the square from h2, the king on b4 seems to be inside and the position looks drawn. This is the most common mistake with the method.
The calculation checks out: with the king on b4 and White to move the pawn queens, with the king on c4 it is a draw. The difference is exactly one file, and the double step is what creates it.
The reverse matters too: with Black to move the same position is a draw - 1...Kc4 gets into the square before the pawn can jump.
The rule of the square answers only one question: can the king catch a pawn that is running on its own? As soon as the stronger side's king joins in, counting the square is pointless - opposition and key squares decide the game.
The calculation: with White to move the position is won, with Black to move it is a draw. The square has nothing to do with it; a different rule is at work - who gets to the square in front of the pawn first.
This mechanism is covered on its own page: opposition in chess. It also explains key squares and why in a pawn ending the king walks in front of the pawn rather than behind it.
An edge pawn is a special case. Even when the enemy king is too late by the square, it may still reach the corner: the promotion square of a rook pawn sits against the edge of the board, and the king cannot be driven out of there.
The position has been computed: a draw with White to move and with Black to move. The white king cannot make way for the pawn without letting the enemy king out, and every attempt to push the pawn through leads to stalemate.
That is why in endings with an edge pawn the defence often comes down to a single task: reach the corner. On stalemate itself - stalemate in chess.
The rule of the square takes a minute to learn and a week to forget unless you set up positions with your own hands. The quickest way is to open a board, place a pawn and the kings, and play it out to the end several times in a row, switching who is to move.
A ready-made training position - the rule of the square in the board editor. You can build your own setup in the chess board editor: pieces move with a mouse or a finger, and hints show the available moves.
Ask yourself "whose move is it?" before every calculation. With the square it is the only thing that changes the result, and it is exactly what people forget most often.
Count the squares from the pawn to its promotion square - that is the side of the square. Lay off the same number of files towards the enemy king. If the king is inside the resulting square or can step into it on its move, the pawn is caught.
Because from its starting square a pawn can move two squares at once. If you count from the second rank, the king seems to be inside the square, but in reality the pawn jumps two squares and escapes. The rule is simple: a pawn on the second rank counts as if it stood on the third.
No. The rule only answers the question about a lone pawn. Once the pawn is supported by its own king, opposition and key squares decide, and the square tells you nothing about the result.
The promotion square of an edge pawn is in the corner. The weaker side's king gets there in time and cannot be driven out: the stronger king blocks its own pawn, and attempts to break through end in stalemate.
The square counts squares, not obstacles. If a piece of the same colour stands between the king and the pawn, the real route is longer than the calculated one, and the method gives the wrong answer. In such positions you have to count moves the ordinary way.
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Endgames - endgames for beginners, pawn endgames, opposition. Tool - online chess board.
