Please see this thread:

http://ths.gardenweb.com/discussions/2558824/stone-information-and-advice-and-checklists

Scroll down to find information on not only how much support you need but also options.

Thanks buehl. I knew I had seen that support info on here somewhere. So it looks like I will need additional support. The Original Granite Bracket company suggests installing the brackets 16-20 inches apart. Do you think that the legs with that wood piece would be considered enough support for the ends and then I measure 16-20 inches from each to start the first Original Granite Bracket? I'm trying to determine how many of these brackets I will need.

"If my island looked similar to the photo with the wood frame and legs how much additional support will I need?

None, especially if you screwed a 1/4" flitch plate behind the rail between the legs.

"I have an 96" by 45" island with two legs, and an 18" overhang (we are v tall), and instead of brackets, our contractor put in rebar along the 45" length in 2 places to give me support without visible brackets. The rebar was fitted into the plywood layer before counters."

I don't like this detail. First, since you have plywood underlayment, I'm assuming your stone is 2cm. The rebar is much too close to the surface of the stone:

Let's hope there is no sink and/or water anywhere near your rebar, because if there is, it will rust, expand, split the stone, and have to be removed.

Secondly, two rebars over 96" isn't much reinforcement. If you were going to do this with 3cm, you'd want a rebar every 18" or so, not every 32" as you have.

We do have a sink in the island, so your point could be an issue. It was discussed by our GC, his engineer, and his fabricator who said that we'd be okay. The bars were cut into the plywood and cabinets and don't touch the quartz top. It's all in and done, so time will tell and/or prove you right. But we are happy with the lack of brackets/corbels. Joseph Corlett, LLC

Joseph Corlett what is a flitch plate?

"Joseph Corlett what is a flitch plate?"

A piece of flat steel used to reinforce wood framing. I sandwiched one between 2x's when I built a header for a historic porch entablature years ago.