Kapiti Island is a small but conspicuous island about 8 km (5 mi) off the west coast of the lower North Island of New Zealand. It is 10 kilometres (6.2 mi) long, running southwest/northeast, and roughly 2 kilometres (1.2 mi) wide, being more or less rectangular in shape, and has an area of 19.65 km2 (7.59 sq mi).
The island is separated from the mainland by the Rauoterangi channel. The highest point on the island is Tuteremoana, 521 m (1,709 ft). The seaward (west) side of the island is particularly rocky and has high cliffs, some hundreds of metres high, that drop straight into the sea. The cliffs are subject to very strong prevailing westerly winds and the scrubby vegetation that grows there is low and stunted by these harsh environmental conditions. A cross-section of the island would show almost a right-angled triangle, revealing its origins from lying on a fault line (part of the same ridge as the Tararua Range).