The following table provides the approximate value of the chess pieces. We assign a value of 1 point to the basic unit, the pawn. Of course, the king is not included in the table because, in a real sense, it has infinite value.
Use the values in this table as a rough guide. By that, I mean that a rook is roughly worth as much as a knight and two pawns. A queen is worth approximately as much as a rook, knight, and pawn. Two rook rooks are roughly equivilent to a queen plus a pawn. Of course, in most situations, there are many other factors to consider, especially the relative activity of the pieces.
You will also note that the bishop receives a value slightly greater than the knight. The bishop is usually, though not always worth a bit more than a knight. See the special section basic bishop strategy for more information on why this might be so.
Note also that there are many moments when it will be to your advantage to give up or "sacrifice" some material in inorder to gain other advantages. By giving up a pawn, you might gain an important square for your knight or an open file for a rook. By giving up a rook or queen, you might be able to force checkmate. You should therefore use this table of values only as a rough guide and not as the sole consideration in your play.