You can cantilever granite up to 10″ with sufficient support on the fixed end and with a large enough piece. Never cantilever unsupported granite where it might receive excessive stress like someone sitting on a counter or stepping on a counter to change a light bulb. You must have support underneath for these situations. Never put weight or stand on or around cut-outs in the counter, such as the skinny piece in front of the sink or cooktop. You will break the counter. Quartz can go up to 14” unsupported. Infinity brackets are popular for unseen support. We offer these brackets for sale.