Ahunui Atoll is roughly circular in shape and measures 6.5 km in diameter. It has a land area of approximately 5.7 km2 and a lagoon area of 34 km2. Its lagoon is totally encircled by the reef, so that it is not connected to the ocean by a pass. The islands have coconut plantations on them.
Ahunui Atoll is permanently uninhabited, but it is visited occasionally by neighboring islanders. The rarer pipi oysters (Pinctada maculata) are found in its lagoon.