Mānana is a tuff cone with two vents or craters. The highest point on the islet rises to . The island is long and wide and has an area of about . Mānana's only sand beach is a small storm beach on the west to south-west (leeward) side of the islet. This sand deposit, located above the reach of the normal waves, is about wide and curves around to the western side of the island. Another volcanic islet named Kāohikaipu sits right next to Mānana.