Standard Vanity height is approx 34.5". A vessel vanity is approx 31" high. If you cannot remove the legs from your existing vanity then it will have to be replaced or cut down to the correct height. The reason a vessel vanity is lower is because your sink will be approx 3 to 6 inches higher than a standard drop in sink. This may be more work than it is worth. Vessel sinks most often will require a solid surface top, either glass, stone or another type of composite material. The standard laminate vanity top has a particle board substrate which will detiorate quickly at the drain location.