Pulau Mesanak, located 7 miles N of the N end of Pulau Sebangka, has the form of an elbow, of which the long arm extends 4.5 miles in a N and S direction, and the short arm 3 miles E and W. Ridges of hills extend the whole length of both arms, the highest point, 107m high, being where the arms meet.
On the E side of Pulau Mesanak, the coastal reef extends for a distance of 0.7 mile; close to the rocky E point, and connected to it, is Koejoe Island, small but moderately high.
Two rocks which cover at HW lie nearly 0.5 mile off the N side of the island and about 1 mile E of Observation Point, the NW extremity of the island.
Patches of 6.9m lies about 0.1 mile NW of the above-mentioned rocks and about 0.2 mile N of Observation Point.
West of the island, foul ground extends W of Merodong Is land and other islands.
Pulau Mesanak forms the S side of the entrance to Selat Merodong, and the W side of approach to Selat Riau.