The calculator tool is pretty simple and has limited functionality at this time. You can access it by checking the button on the main toolbar:
This brings up the calculator dialog bar:
The view field can be used to easily convert data to differant representations: Binary Octal Decimal or Hex.
Depending on what view mode is selected different input buttons may be available.
If you want to limit the size of the output you can change the size field: for example if you want to limit ouput to fit in one byte, select the 8 bit button.