Pawn -- 1 pawn
Minor pieces:
Knight, Bishop -- 3 pawns
Heavy (major pieces):
Rook -- 5 pawns
Queen -- 9 pawns
King --- whole game.
Possible exchanges of equal value:
1 Queen -- 3 minor pieces -- 2 Rooks -- 1Rook, 1 minor piece and 1 pawn.
1 Rook -- 1 minor piece and 2 pawns.