The calendar doesn't have a fixed width or height. This is actually very good because (1) you don't have to figure it out and (2) it's not dependent on fonts and resolution of the client system.

However, if you do need to set a fixed width and height then you should be able to do so by adding something like the following statements somewhere in your CSS section:

.calendar,
.calendar table { width: 500px; height: 400px; }