From October through to March, the tide is high, so it’s better and easier in places for swimming and snorkelling with the beaches and bays full of water. From April through to September, the tide is low during the day making the beaches wider for sunbathing and beach activities.
Koh Tao, with Koh Nang Yuan, forms a small archipelago with a total area of 19.2 square kilometres. At its widest part, Koh Tao measures 3.4 km and is 7.6 km long. The coastline, which is predominantly steep, rocky shoreline, consists of 11 bays and 10 capes and is 28.6 km long with a surrounding coral reef spanning 8 km. A large percentage of Koh Tao is mountainous in varying degrees with about 30% of flat land. Koh Tao is divided up into three villages, Mae Haad and Sairee on the west coast and Chalok Baan Kao in the south. The eastern part of Koh Tao is steep with cliffs. In contrast, the west slopes down gradually to the sea and the flat areas where the villages are. Koh Tao’s highest point is at 374 metres above sea level and Koh Tao’s mountains stretch from north to south.
Koh Tao was formed through land subsidence of the surrounding area, which is now the sea floor, making the depth of the sea around Koh Tao and Koh Nang Yuan at the most 30–40 metres. Koh Tao has a diurnal tide meaning there is only one high and one low water each tidal day.