As a base minimum, it's highly recommended that the swap space should be equal to the amount of physical memory (RAM). Also, it's recommended that the swap space is twice the amount of physical memory (RAM) depending upon the amount of hard disk space available for the system (although this "recommendation" dates back from a time when physical RAM was very expensive and most Unix systems ran with many processes in swap space - a situation that hardly applies in most situations these days, but ancient Unix/Linux myths like this "recommendation" tend to survive well past their "use by" dates). In reality, if you use hibernation you need what was outlined in the relevant paragraph above, otherwise you need as much swap space as your system will use - which actually may be very little in a modern hardware setup. The only downside to having more swap space than you will actually use is the disk space you will be reserving for it.