Neighbouring provinces are (from north, clockwise) Chumphon, Nakhon Si Thammarat, Krabi, Phang Nga, Ranong.
Geographically, the centre of the province is the coastal plain of the Tapi River, mostly grassland interspersed with rubber tree and coconut plantations. In the west are limestone mountains of the Phuket range which are mostly covered with forest. Khao Sok National Park is there. To the east the hills of the Nakhon Si Thammarat (or Bantat) mountain range start to rise, protected in the Tai Rom Yen National Park.
Many islands in the Gulf of Thailand belong to the district, including the tourist islands Ko Samui, Ko Pha Ngan and Ko Tao, as well as the Ko Ang Thong Marine National Park.