Rule of five

The rule of five applies to certain rook and pawn versus rook endings. It is relevant only when the pawn is protected, normally by its king, and the attacking rook keeps the defending king away from the pawn's file, meaning its vertical column.

How to calculate it

1. Count the pawn's rank, meaning its horizontal row, from the side where it started. A white pawn on its fourth rank contributes 4; an equally advanced black pawn is also counted as being on its fourth rank.
2. Count how many full files the defending king is cut off from the pawn's file by the attacking rook.
3. Add the two numbers. If the total is greater than five, the position is usually won. If it is five or less, it is normally drawn.

The formula captures a simple relationship: a more advanced pawn needs less separation, while a less advanced pawn needs the enemy king kept much farther away. It is not a replacement for calculation. Pawns on the two outermost files, and some pawns on the files beside them, can be exceptions because the attacking king has less room to maneuver.

The rule of three answers a different question. It measures the checking distance needed for frontal defense, while the rule of five combines the pawn's progress with the defending king's lateral exclusion.