M theory extensions of T duality

T duality expresses the equivalence of a superstring theory compactified on a manifold K to another (possibly the same) superstring theory compactified on a dual manifold K'. The volumes of K and K' are inversely proportional. In this talk we consider two M theory generalizations of T duality: (i) M theory compactified on a torus is equivalent to type IIB superstring theory compactified on a circle and (ii) M theory compactified on a cylinder is equivalent to SO(32) superstring theory compactified on a circle. In both cases the size of the circle is proportional to the -3/4 power of the area of the dual manifold.