Castling in chess: rules for short and long castling
Castling is the only move in chess where two pieces move at once: the king steps two squares towards a rook, and the rook jumps over to the square beside it on the other side.
It does two jobs in one move: it hides the king behind its pawns and brings the rook towards the centre.
Short castling
Short castling, or castling kingside, is written O-O. The king goes from e1 to g1 and the rook from h1 to f1 (for Black, e8 to g8 and h8 to f8). Only two squares must be empty, so it is usually the quicker one.
Long castling
Long castling, or castling queenside, is written O-O-O. The king goes from e1 to c1 and the rook from a1 to d1. Three squares between them must be empty: b1, c1 and d1.
When you cannot castle
Castling is allowed only when all of these are true:
- The king and that rook have not moved yet in this game, not even to come back.
- The squares between them are empty.
- The king is not in check. Castling is not a way out of check.
- The king does not pass through an attacked square or land on one. The rook may pass an attacked square.
Exercise: castle
White wants to get the king to safety. Castle in the only way the rules allow.
Make the move on the board: drag a piece, or click it and then a square.
Solved!
O-O-O. Short castling is not allowed, because the king would pass through f1, which the bishop on c4 attacks. On the queenside b1, c1 and d1 are empty, and the king’s squares are safe.
Key points
- Castling moves the king two squares towards a rook; the rook jumps over to the other side.
- Neither piece may have moved, the squares between them must be empty, and the king may not be in check or cross an attacked square.
- Castle early: it is the quickest way to make the king safe and bring a rook into play.