A slice is just one piece - on that I think we all agree.
A round though, Is not a definitive measure. A round is how much you make at the time, so depends on how hungry you are and how many people there are.
Pretty much like a round of drinks is one drink fior each person (although if you are buying a pint and a shot for each person, that is still just one round even though twice as many drinks are invoved).
As a toast expert, and let's face it - eating toast raw is a disgusting habit, then I believe it can be illustrated as follows.
If made myself a round of toast, I could have just the one slice, or two (or quite possibly more).
If I had just come back from the pub, and had a mate with me and I suggested a round of toast - then I daresay I would make 4 pieces. Then probably would go for a second round (ding dong - seconds away).
The reason for 4 is more a limit to the toaster capabilities than the maximum slices in a round.
If Ihad a larger group of people at the house, and I suggested a round of toast, then I daresay one for each person would be expected in such an extravagant round (yes I know, we really know how to party in my house).
Hopefully that answers your question. You know I am right.
