Width / Height
The grid of squares in the top left of the palette represents the sides and corners of the bounding box of the selected object(s).
Click on one of the squares to select it (turns black). The X: Y: values will change to show the coordinates of that corner, side or centre of the bounding box.
Enter new values for Width: or Height: and the size of the selected object(s) will change relative to the currently active grid-square.