That needs to be answered by your fabricator because of layout, shop processes and other factors.

cluelessincolorado:

I can't disagree with kevdp4.

I need to know that you're not attempting stone slab fabrication as a do-it-yourself project. You can nail down three tab roof shingles and even wire an outlet from internet videos and following manufacturer instructions without endangering yourself or yours. No so with stone slabs.

ROTFL!!! No, I am NOT attempting to do any DIY fabricating, cross my heart :-)
I agree with contacting the fabricators, but I was looking for a very general (conservative) amount. 6", 10", that kind of guidance for layout.
Thanks!