The basics. 1 semester course for each.

I'd say slightly more. Maybe it's just because I attended a state school, but I think my first semester calculus class was all single variable (20 years ago now, so my memory is rusty). You really to understand gradients and jacobians for ML, which I think was calc III for me. But you can skip curl and div part I guess.

Oh, that’s right. Multivariable was Calc II for me so technically two semesters.

how much of that do you really use for ML

Not much of your calculus book will be relevant beyond the first couple of chapters, but you'll live and die by the numerical-method sword. The idea is that you need the analytic insight from the former to understand the latter.

I don't know if I really buy that, though.

thanks! I wonder if someone has compiled a resource with just enough math for ML.

I believe fast.ai does this - they start with you using real tools and teach you the foundation as it becomes relevant