The numerical value of each piece is one of the first thing you learn when you pick up chess.
A rook is worth 5 points and a bishop only worth 3 points.
But why is the rook better than the bishop?
The rook moves linearly and the bishop moves diagonally. So how can the rook be worth 2 points extra when their movement is so similar?!
Let’s go over the reasons why a rook is more powerful than a bishop.
1. Can go to all squares
Both the rook and the bishop are long-range pieces that can move as many squares as they want.
The big difference is that rooks move linearly and the bishop move diagonally.
As a result, a rook can move to both black and white squares, while a bishop can only move to squares of the same color.
This means that rooks can control all the squares on the board, while a bishop can only influence half the square on the board.
2. Always controls 14 squares
Since a rook moves linearly and the chessboard is a square, the rook always controls 14 squares on an empty board.
So the rook will be just as strong in the center of the board as in the corner.
When a bishop is placed in the center it can control 13 squares, only 1 square less than the rook.
But the bishop controls fewer squares the further it is away from the center. And when a bishop is in the corner of the board, it only controls a measly 7 squares, that’s half of what a rook controls in the corner.
3. Can checkmate together with the king
A rook and king can checkmate another king together, while a bishop and king can’t.
So if you end up in an endgame of bishop and king against a king, the game will still finish in a draw despite you having an extra piece!
Similarly, a pair of rooks can checkmate a king by themselves, while a pair of bishops needs the help of a king to force a checkmate.
However, that’s still better than a pair of knights which can’t checkmate even with the help of a king.
4. Can castle with the king
Although it’s a move that most beginners overlook, a king and rook can castle. This both brings the king to safety and activates the rook.
Castling is so important, that you probably want to make use of it in at least 95% of your games.
There is no special move that you can do with the king and bishop together.
5. A pair of rooks can coordinate an attack
Since a rook can move to any square on the board, that also means that both rooks can attack the same square. This is especially devastating when your two rooks penetrate the 7th rank and start gobbling up all the pawns.
On the other hand, bishops can never attack the same target because they are bound to squares of the same opposite colors.
6. A pair of rooks can defend each other
Being able to move to the same squares also gives a pair of rooks the ability to defend each other, while a pair of bishops can never defend each other.
In the diagrams below, you can see that the rooks are safe from any double attacks by the black queen because they can defend themselves, while the two bishops can’t help each other.
7. A rook can cut off the king
A very important feature of the rook is that it can completely cut off the opponent’s king along a file or rank. While a single bishop can’t contain an opponent’s king at all.
Being able to cut off the king is a very important motif in the endgame. In the endgame, your king becomes an important piece in the attack, and by cutting off your opponent’s king you are basically playing with one piece extra.
8. A rook can capture a pawn trying to promote
Both the rook and pawn move linearly. This means that a rook can attack a pawn and the only movement square for the pawn. So a rook can easily capture pawns that are trying to move down the board and promote into a queen.
But a single bishop can’t capture a pawn by itself. If the bishop attacks a pawn, the pawn simply moves forward one square to safety. But if you prevent the pawn from moving by attacking the square in front of it, you won’t be able to capture it.
The rook is better than the bishop because it can move linearly instead of diagonally. As a result of this difference, the rook can control both black and white squares, control more squares at the same time, and can force a checkmate together with a king.
Other benefits of the rook such as being able to cut off a king or controlling pawns are more circumstantial.
All of that being said, the value of a piece always depends on the concrete position on the board. It is possible that in some positions, the bishop is actually move valuable than the rook.
So always take into account the relative piece value in the position, instead of simply looking at the numerical value of each piece.