The size of swap space should be larger than the physical memory size.
Actually, there is no magic "formula".
A standard version of A/UX 2.0, based on an A/UX with 8MB of physical
memory, has about 18MB of disk space allocated for swap purposes. 18MB is
twice as much as the physical memory. Therefore, if disk space is not a
restraint, we recommend two to two and a half times the physical memory size
be assigned for swap space. If disk space is a concern, less than twice of
physical memory size may be allocated for swap space.
Note that the swapping in and out activity occurs only when the available
physical memory is used up. If your applications require large amounts of
memory allocation, you should increase the swap size. Use the "swap -l" to
view the current free swap size. If you have a reserved A/UX partition,
you may use the "swap -a ..." to add additional swap area.