The size of the box depends on the lenght of the words in the box. If you only use 8 letter words, then the box will only be 8 letters long. You could make a minimum width by adding black non-breaking spaces to the end of one of the items so foarcing the width out. But it wouldn't realy be right to make the box smaller than the text it contains. The text box has the character size included because it is usually empty by default.
You could also set the font size using css. If you want a smaller box, use a smaller font size.