Koh Samui is located in the Gulf of Thailand (bordering the South China Sea in the Pacific Ocean). The island is in the Surat Thani province.
It is the most significant island in the Chumphon Archipelago. The island measures some 25 km at its widest point. To the north are the populated resort islands of Ko Pha-ngan, Ko Tao, and Ko Nang Yuan.
The central part of Ko Samui is the generally tropical jungle, consisting of its largest mountain, Khao Pom, peaking at 635 meters. The most famous landmark of Koh Samui, the Big Buddha.