In designs where your countertop spans supports, the length of the span (side to side as your facing it) should be limited to 24" for ¾" (2CM) thick stone and 36" for 1¼" (3CM) stone thicknesses.
For designs where your countertop is cantilevered or overhangs the supports, overhanging portion should be limited to 6" for ¾" (2 CM) thick countertops and 10” for 1¼" (3 CM) stone countertops.
The overhang should never be more than 1/3 of the depth of the countertop (front to back as your facing it). Cantilevered countertops exceeding these dimensions require corbels or leg support underneath the stone.
Note: Fragile stones may require corbels and supports that are spaced closer together and that do not allow as much overhang than the specifications here. Click to see how to support quartz countertops vs. granite. Learn about a granite warranty.