I have just bought a lamp-post for my front garden to replace a small
pedestal that had been knocked over too many times.
I am planning to make a base for it to stand on using threaded rod and
angles buried in concrete.

1. how deep does it need to be?

2. Should I use stainless steel, or will mild be good enough for this
purpose?

3. How do I work out how much concrete to mix? considering that bags of
cement and ballast are sold by weight and holes in the ground are
measured by volume?

thanks

dan