How to get volume from an open surface

Hello! I know this might be really silly but im trying to get the volume that exists between the circular plane and the piece above it, and do the same with the one below the plane. Is it possible to measure that? I’ve done the splitting already so i have every piece separated.
In worst case scenario, how can i get the volume from the hole surface, forgetting the plane in the middle?
I would really appreciate any help possible. Thanks in advance!

There is no such thing of a volume when the surface is open, do you mean something else?

Probably need to close the wavy surface, split it with the round plane then get volume of each one.

thanks! thats exactly what i needed.