A:Answer The usable surface is just under 11 inches (10 7/8").
[I think you may be able to use larger dishes than that, but not sure about the weight it can hold.]
If the dish you are using covers the buttons, you can still control it from the smartphone app.
It boils water just fine.
I haven't tried boiling water in my 10-inch 6 qt, but I did deep fry in it.
In fact, it heated a 6qt pot of oil to 350 so fast I was deep frying french fries in about 10 minutes. Oil got cold-ish, but one top was able to keep up.
Hope this helps.
