RAM or EPROM?
RAM is used for stack (local variables, parameters, etc) and transient objects. EPROM may contain code and object instances.
Anyway, occupied size in RAM or EPROM depends on implementation of Java Card.
Size in EPROM is approximately the same as size of all components of cap file excluding descriptor.cap.
Approximate RAM requirements can be calculated using specification. Each method parameter and local variable occupies 2 bytes (int values - 4 bytes). Each method call takes 6-8 bytes on stack.