How to get required size to install TestExecute dynamically at silent mode before installation?

Yes we know the system requirements and we know the required disk space . But in my case we installing TestExecute using NSIS Script as a Silent installation and we don't want to hard coding required disk space. 
 
Can we get required disk space dynamically before installing TestExecute.exe by passing any commands to it.? 
 
Because every time new version of TestExecute will come and we need to change the code eventually. If at all any command exist to get required disk space of TestExecute , its very helpful