Swap will be 2x RAM;
This is actually a very old sizing rule and I think it's obsolete. On modern systems (i.e. with 1GB or more of RAM), I give 1x RAM for Swap.
boot will be ~200M.
Wow! How much kernels do you plan to use, 20? For most users, 50Mo is enough.
How much should the OS
receive? I was thinking of giving it
between 15 and 20G (and all else to
/home where most of my files will be
located), but I wasn't sure if it
would need more.
Is there a standard way of determining
the partition size for '/'?
I don't know a "standard" way as it highly depends on how much software you'll install and
what you'll be doing with your computer. A server install (mail, database...) will typically use a pretty big separated
/var partition. For a personal machine, this is most of time useless. In fact, 10 GB for
/ should be more than enough for most users. If you plan to install many (and I really mean many) packages, you might need some additional GB, but not more than 15 GB. If you plan to install external softwares (e.g. in
/opt), take it into account (I personally have many Java stuff installed in
/opt, like commercial app servers that are not really lightweight). If you are going to rip DVDs, add a few more gigs. And indeed, use the rest of the space for
Actually, you should now understand why it's hard to give an absolute answer and experience (i.e. trial error) is the best way to find the "perfect" sizing for your machine. But even for an experienced user, needs might change with time. That's why, as someone pointed out, LVM and resizable filesystems are weapons of choice to avoid any pitfalls.