Basically they recommend 28m diameter if you are going to have a central island, otherwise it should be a mini-roundabout (capable of being driven over)
I’ll add that in my family’s home town (farming town in Perthshire) in Scotland, there are mini roundabouts that are just a spot of white paint in the middle of the intersection. It works fine.
Basically they recommend 28m diameter if you are going to have a central island, otherwise it should be a mini-roundabout (capable of being driven over)