Pop rivets or structural rivets. it doesn't really matter on pop rivets you just have more sticking out on the other side. Structural however do have a range, and that depends on the rivet. Hemlock or ... cant remember other make, usually stamped on the head top, though often very hard to see
For countersunk rivets it will be from the top of the head, rather than the underside. Sometimes they specify the thickness of the head too, but not often, even then, grip length will still be including the head for csk ones.