i found it very usefull

http://ikariamlibrary.com/?content=Army%20Calculator%20Spreadsheet

The purpose of the first page is for the main section to be filled in and saved and adjusted as needed so as to keep a personal reference to monitor the defense capabilities of each of your towns, your generals score and upkeep with each proposed change in military units. The second section allows you to assess the costs of your intended military expansion and will indicate how much generals score you will gain and how much your upkeep will rise as a result.

The purpose of this page is to give you an estimate of your oppositions defense prior to a battle taking place to to allow you to send an appropriately sized army. Or if you wish to calculate the defense of your own town to assess the minimum army size required to pillage you (worst case scenarios). If you have an idea of the structure of an attack heading your way you can use this to assess the likelyhood of the attack being successful.