When should I create new files for class? [closed]

  adapter, c++, design-patterns, header-files

I am trying to implement an adapter pattern in my program.
I have a class that can return me its size in inches, and I want to convert it to meters. So I create 2 more classes – the virtual interface and the adapter itself. Am I supposed to create new header and cpp files for each of these classes? Or is it fine to put them in one file?

Source: Windows Questions C++