Unfortunately, no. There is no such standard. Here are a few reasons why.
- There are a lot of ambiguities: outdoor space, the area between interior walls, etc.
- In most cases, measuring is difficult since apartments rarely have simple shapes
- In my view, it really does not matter so much anyway. What matters more is whether the layout allows you to use the space for what you want: room for children to play? closet space? big kitchen if you like to cook?
I think too many people focus on square footage. Even if it were reliable, I don't think it really tells you all that much.