As deep as your stool seat and room for knee clearance for any corbels. I wish my overhang was a bit deeper myself. Also, if you have granite, do not forget to get the heavy gauge steel plate under the entire counter top for support. Here's a photo (during the modification of cabinets and failed finish) of the metal plate that is probably bullet proof thickness!

If you do not use a metal plate, (some people use plywood, which brings other problems), then your granite could crack should someone plop their fanny up on the counter to sit when you're not there and it not have proper support. Things go on in your home when you're not there and kiddos are left alone... no matter what their ages! I know of a teen boy that jumped off an island counter years ago and the counter cracked because it did not have proper support. It fell a few minutes later. And corbels or L brackets are not real support; they are decorative.

Here is a link that might be useful:

I don't know...we are doing 12 because that's all we have room for and I've read that's really the minimum. 24 seems like a lot to me though so I'd probably go with 18 if space were not an issue. I'm sure those more experienced will chime in!

Sherilyn,
Thanks for the info on the metal plate. I didn't know about that. I'll have soapstone & I really like the streamlined look of the metal plate better than brackets or corbels (although I LOVE your corbels...WOW).

My kids are getting to the age where they'll be spending more time at home alone and I am afraid to say that I can envision the countertop turn into a skateboard ramp.