200 x 200 x 200 mm cube at 0.0635x0.0635x0.1 mm/pixel resolution is 40GB. If you want to make sure that you don’t run into memory allocation error then allocate 10x more memory space than the size of your data set is, which in this case is about 400GB.
I would recommend to start small. See if everything works if you work with smaller volumes (larger voxel size) and check everything works well and what your peak memory usage is. Then you can gradually reduce the voxel size to find a good tradeoff between accuracy and memory usage (and computation times).
Can you tell a bit more about your application? What kind of data are you working with and what is your overall goal?