This crater is located at the origin of an extensive ray system that extends for several hundred kilometers across the surrounding lunar terrain. The exterior surface for about 20-30 km is relatively free of the ray material, but beyond that perimeter is a skirt of higher albedo, with streaks extending to the northwest, east-northeast, and southward.
The outer rim of Ohm is sharply defined, except at the southern end where the edge is somewhat irregular. The inner surface drops down to an interior blanket of slumped material that slopes down to the floor. The crater lacks a notable central peak at the mid-point.