Phuket is the biggest island in Thailand, located in the Andaman Sea  off southern Thailand. The island is mostly mountainous with a mountain range in the west of the island from the north to the south. The mountains of Phuket form the southern end of the Phuket mountain range, which ranges for 440 km from the Kra Isthmus. The highest elevation of the island is Mai Thao Sip Song (Twelve Canes), at 529 m above sea level. It is estimated that Phuket has a total area of approximately 570 square kilometers (including the provinces other islands). The main island’s total length, from north to south, is about at 50 kilometers and approximately 20 kilometers wide.

Forest, rubber and palm oil plantations cover 60% of the island.  The western coast has several sandy beaches, while on the east coast beaches are more often muddy. Near the southernmost point is Laem Promthep (Brahma's Cape), which is a popular sunset viewing point. In the mountainous north of the island is the Khao Phra Thaeo Non-hunting Area , protecting more than 20 km² of rainforest . The three highest peaks of this reserve are the Khao Prathiu (384 m), Khao Bang Pae (388 m) and Khao Phara (422 m). The Sirinat National Park on the northwestern coast was established in 1981 and protects an area of 90 km² (68 km² marine area), including the Nai Yang beach where sea turtles  lay their eggs.

One of the most popular tourist areas on Phuket is Patong Beach  on the central western coast, perhaps owing to the easy access to its wide and long beach. Most of Phuket's nightlife and its cheap shopping is located in Patong, and the area has become increasingly developed. Patong means "the forest filled with banana leaves" in Thai . Other popular beaches are located south of Patong. In a counterclockwise direction these include Karon Beach, Kata Beach, Kata Noi Beach, and around the southern tip of the island, Nai Harn Beach and Rawai. To the north of Patong are Kamala Beach, Surin Beach and Bang Tao Beach. These areas are generally much less developed than Patong, and sought out by individuals, families and other groups with a preference for more relaxed and less crowded environs than Patong. There are many islands to the southeast, including Bon Island, just a short boat trip away. There are several coral islands to the south of Phuket, the Similan Islands lie to the north west, and Phi Phi islands to the south east. Islanders engage in a lively tourist trade, catering to snorkellers  and scuba divers.