Located 220 km from the capital in the Gulf of Thailand, Ko Samet is approximately 13.1 square kilometres (5.1 sq mi) in size, and shaped somewhat like the letter "t". Along the length of the "t" (north-south) the island measures approximately 7 km, and measures 4 km across the "t" (west-east). Forests blanket up to 80 percent of the total area.[citation needed]
Ko Samet is one of the driest archipelagos in Thailand. Ko Samet gets significantly less rainfall than Rayong Province, even though it is only a few kilometres offshore. The island's "rainy season" extends only from May to July, but even during this season it has less rain than other islands in Thailand. The island, despite being arid, consists of lush forested hills, covered with evergreen and deciduous forest and cajeput trees grow abundantly (the name "samet" means "cajeput"). Owing to the lack of rain, Ko Samet must import potable water from the mainland.