I have 512mb of memory how big of swap file do I need?

usually 2-3 times of your memory size

I think 2-3x is an old standard. I have 256 megs in my box, and only use a swap partition of 128 megs. I think once you're have > 128 MB RAM, 1x swap should be plenty.

Garry

I don't push my box hard and run a slim Slack but I have 512 and usually hover in the 50% range without ever touching swap. I have 512 and, unless you're doing radically RAM-heavy stuff, wouldn't recommend any more.

I'm playing around in 10 now (so it's still a-building) and I've got:
That's remarkably low even for me, but still - a gig of *total* RAM 'is more than enough for anybody'. The 2 times thing is outdated - and I've never heard 3. So put me down in major.tom's camp. 128,256,512 - whatever you want for some leeway, but no need to waste a lot of disk space on slow fake RAM.

One nice thing about a swapfile instead of a swap partition is that you can change the size and experiment. my mini- distros that use windowmaker will easily run with 16MB RAM and 8MB swap. FFor the browser to have any cache, obviously more swap is needed. And if you run KDE or gnome you'll need more.
In your case 64MB should more than enough. People who do video editing or are 'remastering' ISO's may need up 3x the size of what they are working on. For instance to remaster a CD ISO of 700MB you will want at least 1.5GB and possible 2.1 GB.
Some people try to run without any swap at all, but this is not agood idea, either, since the kernel expects to find swap space and will tra to use it for a few bytes even if you have lots of RAM. Take a tip from ZipSlack and have at least a 512K swapfile around somewhere.

I have 512 mb and no swap file!

free
total used free shared buffers cached
Mem: 515480 210148 305332 0 20524 119776
-/+ buffers/cache: 69848 445632
Swap: 0 0 0

many people notice no problems running with no swap, but as I've said before a bit of swap is linus' security blanket, he doesn't REALLY need it, but he does like to know it's there. If you have a way of testing, you may notice a performance improvement throught the use of a swap file of even 4K which is the minimum size recognized by the kernel. On some systems the kernel will actually spend quite a lot of time looking for a few bytes of swap space.

If you plan on using suspend or software suspend you will need at least 1x the amout of your ram.
As a rule of thumb, I always do this. . .

64 megs of ram and lower = 3x swap.
96 megs to 256 megs of ram = 2x swap.
384 megs to 768 megs of ram = 1x swap.
768 megs and higher = .5x swap (unless you want to suspend to disk or software suspend)

From everything I've read so far, while you can get by without any swapfile if you have enough RAM, it is usually a good idea to have a swapfile size of around 512MB total, which can be split up into smaller sizes for each hard drive you have.................For example, I have two swapfiles on two hard drives of 256MB each.......................