Koh Samui The 247-square-kilometre Samui island is Surat Thani's major tourist attraction. Located 258 nautical miles south of Bangkok, and some 84 kilometres east of the provincial capital, Koh Samui measures some 21 kilometres at its widest point, and 25 kilometres at its longest. A 51-kilometre ring and largely coastal road encircles the island, which has numerous lovely beaches and bays, and is almost literally an island of coconuts and forested hills.