What is the size of counter strike source?

This depends on how much script and skins you've putted in your cstrike folder. You can see how big it is by yourself by doing this: go to your drive where you stored Counter-Strike:Source usually here: C:\Program Files\steamapps\YOUR LOGIN NAME\ Right-click the cstrike folder and go to properties then it will show you how big your cstrike is. Hope this is the right answer for you question.