How to calculate memory band width ?

How to calculate global memory band width，such as mali-T864 and mali-G52 Mp4?

1、In my past opinion mali-T864 ddr bus width is 64，all core shareing this bus width,ddr frequency is 800MHz, dual channel,so its memory band width is 0.8GHz*64bit/8*2=12.8G/s.It is independent of the core number.But when I read the blog"The Mali GPU: An Abstract Machine, Part 3 - The Midgard Shader Core",it said "The GPU will typically have 32-bits of DDR access (read and write) per core per clock [configurable]",I am very confused,according to this blog,band width is related to the number of cores,each  core can read and write per clock.

2、How to calculate mali-G52 mp4 memory band width?