In physics there is a differentiation made between "vacuum" and "void". From an article entitled "How Feynman Diagrams Almost Saved Space" by theoretical physicist Frank Wilczek:
Vacuum, in modern usage, is what you get when you remove everything that you can, whether practically or in principle. We say a region of space “realizes vacuum” if it is free of all the different kinds of particles and radiation we know about (including, for this purpose, dark matter — which we know about in a general way, though not in detail). Alternatively, vacuum is the state of minimum energy.
Intergalactic space is a good approximation to a vacuum.
Void, on the other hand, is a theoretical idealization. It means nothingness: space without independent properties, whose only role, we might say, is to keep everything from happening in the same place. Void gives particles addresses, nothing more.
Aristotle famously claimed that “Nature abhors a vacuum,” but I’m pretty sure a more correct translation would be “Nature abhors a void.”
In this view, vacuum refers to an actual region of spacetime. Remember that quantum field theory tells us that there are fields that exist all throughout the universe. Even if you remove particles from a region of spacetime the fields themselves still exist in those points, they are just in a minimum energy state so there is no actual particle or radiation in that space. If you were to put a field vacuum inside of a box (build a box around a particular region of vacuous spacetime?) then that region would still have a dimension of length, because it is still spacetime that is permeated with minimum energy field vacua.
On the other hand, a void is the idea of a region of space and nothing else. It doesn't have minimum energy field vacua, it doesn't even have a time component. It is the abstract concept of just having a region of space. If you were to have a box that had a void inside of it it would still have a length because it is the definitional concept of space. From Wikipedia:
Space is the boundless three-dimensional extent in which objects and events have relative position and direction.
Even in a void, a theoretical region of space that has nothing inside of it, it still has spatial dimensionality because it is, by definition, space.
A third concept, the concept that you are most likely meaning to refer to, is the idea of an absolute nothingness. Nothingness, or emptiness, is what is called a universal, or an abstract concept. There isn't a region of the universe you could go to that would contain nothingness because all regions of the universe have spatio-temporal dimensionality. So you wouldn't ever be able to find a region of actual "nothingness" to enclose. However, that brings up the problem of universals vs particulars, or even just abstract objects in general. Here are two introductory resources that will help you get a better understanding of the subjects: Properties and Abstract Objects. It is not a closed debate about whether or not universals, such as "nothingness", or abstract objects in general exist. There are good arguments on both sides and this is a question that has been discussed at the forefront of western philosophy since Plato and Aristotle. Whether or not "nothingness' as a universal exists, you still would not be able to encapsulate it within a box. As for vacua and voids, however, both of those do have dimensionality because both of them are bounded by spatial dimensions.
To state definitively and succinctly: a vacuum would have a size of one cubic meter in your example; a void would have a size of one cubic meter in your example; the abstract concept of "nothingness" would not have any sort of size and could not be put into a box because it refers to the abstract concept of nothingness. Hopefully now it makes more sense why the definitions you chose really matter and a question such as "If 'nothing' is encapsulated by 'something', does this imply it has size?" at face value is a little vague.