39gb if you use a fp8 quantized model.[1] Remember that your OS might be using some of that itself.
As far as I recall, Ollama/llama.cpp recently added a feature to page-in parameters - so you'll be able to go arbitrarily large soon enough (at a performance cost). Obviously more in RAM = more speed = more better.
The quantized model fits in about 20 GB, so 32 would probably be sufficient unless you want to use the full context length (long inputs and/or lots of reasoning). 48 should be plenty.
I‘ve tried the very early Q4 mlx release on an M1 Max 32GB (LM Studio @ default settings), and have run into severe issues. For the coding tasks I gave it, it froze before it was done with reasoning. I guess I should limit context size. I do love what I‘m seeing though, the output reads very similar to R1, and I mostly agree with its conclusions. The Q8 version has to be way better even.