You can use this free app to calculate SWG/AWG number of required wire for carrying given value of current specifically for transformers and turn per volt for a transformer. In transformer winding we have to find out SWG/AWG number of required wire for given value of current. After finding turn per volt value you can easily find out turns for each loop/coil of transformer. How to use this app? For details go to http://www.micro-digital.net/transformer-winding-calculator/