As a general rule, also the amount of physical memory installed in a computer should be proportional with the number of hardware threads provided by its CPU.

Besides the fact that the operating system may allocate some memory for each thread, when you launch a multi-threaded application that is able to use all available threads, for instance the compilation of a big software project, it frequently will allocate some working memory in an amount proportional with the amount of working threads.

I have encountered many multi-threaded applications that need up to 2 GB per thread to work well.

This corresponds to having 64 GB for a desktop CPU with 32 threads, like Ryzen 9 9950X.

For the compilation example, I have seen software projects, like Chrome/Chromium and its derivatives, where if you do not have enough memory, proportional to the number of hardware threads, e.g. when you have only 32 GB for a 16 core/32 thread CPU, you must reduce the number of concurrent compilations, e.g. with an appropriate parameter to "make -j", leaving some threads and cores idle, because otherwise you may encounter out-of-memory errors.