That depends on what you are buying. Here most granite tops are sold at a full 1 1/4 thick. They install on top of the cabinets ( with proper support for overhangs ). There are areas where the tops are sold at 3/4" thick and have a build up edge - these will usually have some sort of plywood sub straight underneath to make up another 1/2 - 3/4" so they look like full thick tops. This same idea applies to folks who are doing thicker tops.

Good luck!

If they are existing cabinets or an old home you must make sure they can handle the weight of the stone. The cabinets must be perfectly level as well. Double check all of that before putting down any money on material...

2 or 3cm granite can be installed without a substrate, directly on cabinets. The cabinets must be pretty level; the top installer will have final shimming on even perfectly leveled cabinets as stone isn't consistently thick and bows sometimes.