The official answer is 936 islands, the figure used by Thailand's Department of Marine and Coastal Resources (DMCR), the government agency responsible for the coast. That figure comes from a survey published in October 2008; 562 of the islands are on the Andaman Sea side and 374 in the Gulf of Thailand, and the largest by far is Phuket.
Most of the 936 are small: rocks, islets and wooded outcrops with no people and no beach to speak of. Hotels and guesthouses exist on perhaps a few dozen, and just six are larger than 100 square kilometers. This page sets out the official numbers, where they come from and which islands are the biggest. If you are trying to decide which island to visit, our guide to choosing the right Thai island is the better starting point.
Thailand's islands in numbers (DMCR)
- Total islands
- 936, in 19 provinces
- Andaman Sea
- 562 islands in 6 provinces
- Gulf of Thailand
- 374 islands in 13 provinces
- Combined land area
- 2,686.84 km²
- Combined coastline
- 3,724.32 km
- Islands over 100 km²
- 6
- Islands inside marine national parks
- 491, just over half
- Year of the survey
- Published October 2008; repeated by DMCR in 2018
Where the figure of 936 comes from
The number comes from a DMCR book titled "Diversity of Islands in Thailand" (in Thai), published by its Marine Resources Conservation Division in October 2008. It records 936 islands in Thailand's seas, spread across 19 coastal provinces. The department still uses the same figure in its online knowledge base and repeated it in an infographic in 2018. We found no newer official count, so 936 remains the official answer as of October 2026.
You will see other numbers online. DMCR's own database mentions an earlier 2004 study by Chulalongkorn University that counted "more than 700" sea islands on the Royal Thai Navy's nautical charts, which used a different method. Other totals you may meet on travel sites have no official basis that we could find.
The count covers islands at sea. It includes a handful in Songkhla Lake, the large coastal lagoon in the south, but islands in rivers are not part of it. And because the survey dates from 2008, it cannot show any changes to small islets and sandbars since then.
The six largest islands, ranked
The DMCR gives exact areas for the six islands larger than 100 square kilometers. Together they cover just over 1,347 square kilometers, about half of all the island land in Thailand.
| Rank | Island | Area (km²) | Province | Sea |
|---|---|---|---|---|
| 1 | Phuket | 514.675 | Phuket | Andaman |
| 2 | Koh Samui | 236.079 | Surat Thani | Gulf |
| 3 | Koh Chang | 212.404 | Trat | Gulf |
| 4 | Koh Tarutao | 150.84 | Satun | Andaman |
| 5 | Koh Phangan | 122.017 | Surat Thani | Gulf |
| 6 | Koh Kood (Koh Kut) | 111.894 | Trat | Gulf |
Two of these rankings are often wrong online. Koh Chang is the third-largest island, not the second; Koh Samui is larger. And Koh Kood is sixth, not fourth, because the national park island of Tarutao and Koh Phangan are both bigger.
Phuket island is 514.675 km², not 543 km². The larger figure you often see is the area of Phuket province, which also includes 36 smaller islands around it. The island itself is the DMCR figure.
The six in a sentence each
Phuket is linked to the mainland by bridge, has an international airport and is, in practice, a city with beaches. Koh Samui has its own airport and is the hub of the Gulf islands. Koh Chang, near the Cambodian border, is mountainous and reached by car ferry. Koh Tarutao is a national park with no village and only park lodges, next to Koh Lipe. Koh Phangan sits between Samui and Koh Tao. Koh Kood is the quiet, forested island at the far end of the eastern chain.
Andaman or Gulf: how the islands split
The Andaman side, Thailand's west coast facing the Indian Ocean, has fewer provinces but more islands: 562 across Phang Nga, Krabi, Satun, Ranong, Trang and Phuket. Many of them are the limestone towers of Phang Nga Bay and the Krabi coast. The Gulf side has 374 islands spread over 13 provinces, from Trat near Cambodia to Narathiwat near Malaysia.
| Province | Islands | Sea | Largest islands (DMCR) |
|---|---|---|---|
| Phang Nga | 155 | Andaman | Koh Phra Thong, Koh Yao Yai, Koh Kho Khao |
| Krabi | 154 | Andaman | Koh Lanta Yai, Koh Lanta Noi, Koh Pu (Koh Jum) |
| Surat Thani | 108 | Gulf | Koh Samui, Koh Phangan |
| Satun | 106 | Andaman | Koh Tarutao, Koh Tammalang, Koh Tabeng |
| Trat | 66 | Gulf | Koh Chang, Koh Kood, Koh Mak |
| Ranong | 56 | Andaman | Koh Sai Dam, Koh Chang (Ranong), Koh Phayam |
| Trang | 54 | Andaman | Koh Libong, Koh Sukorn, Koh Mook |
| Chumphon | 54 | Gulf | mostly small islets |
| Chonburi | 47 | Gulf | Koh Khram, Koh Si Chang, Koh Larn |
| Phuket | 37 | Andaman | Phuket, Koh Sire, Koh Racha Yai |
The other Gulf provinces have fewer: Prachuap Khiri Khan 23, Chanthaburi 19, Phatthalung 18 (all in Songkhla Lake), Rayong 16 (the largest is Koh Samet), Nakhon Si Thammarat 9, Songkhla 6, Pattani 4, Narathiwat 3 and Chachoengsao 1. Phang Nga and Krabi alone hold a third of all Thailand's islands.
The split matters for travel because the two seas have opposite weather. On the Andaman side the dry, calm months run from roughly November to April, while the Gulf islands around Samui stay drier in the middle of the year. Our page on the best season for each group of islands explains the pattern.
Two islands called Koh Chang, and other name traps
With 936 islands, names repeat. There are two well-known islands called Koh Chang ("elephant island"): the big one in Trat, third-largest in the country, and a much smaller one in Ranong on the Andaman coast. Koh Samet is the familiar holiday island in Rayong, but Chumphon also has a Koh Samet. Koh Mak in Trat is a holiday island; Phatthalung has another Koh Mak in Songkhla Lake.
Some islands also have two names. The DMCR lists "Koh Pu" among Krabi's largest islands; most travelers know it as Koh Jum, the quiet island between Krabi and Lanta, where the northern part is called Koh Pu. When you book a boat or a room, check the province as well as the island name.
Most islands are protected, and most are empty
Just over half of the islands, 491 of 936, lie inside marine national parks, such as the Similan Islands, Tarutao and Ang Thong off Samui. Many others are under local government, and some are used by the Royal Thai Navy for bases, lighthouses and monitoring stations; in Chonburi, nearly half of the islands are under navy control.
Very few have permanent villages. That is why a trip "to the islands" usually means a handful of names: Phuket, Samui, Phangan, Koh Tao, Phi Phi, Koh Lanta, Koh Chang, Koh Samet, Koh Lipe and a growing list of quieter places such as the Trang islands. Our overview of Thailand's islands introduces the ones with places to stay, and our island-hopping guide explains how to travel between them.
Frequently asked questions
How many islands does Thailand have?
The official figure is 936, from a survey by the Department of Marine and Coastal Resources published in October 2008: 562 in the Andaman Sea and 374 in the Gulf of Thailand, across 19 provinces. No newer official count has been published.
What is the largest island in Thailand?
Phuket, at 514.675 square kilometers according to the DMCR. It is more than twice the size of the second-largest island, Koh Samui (236.079 km²). Phuket is connected to the mainland by road bridges and is also a province in its own right.
Is Koh Chang bigger than Koh Samui?
No. Koh Samui covers 236.079 km² and Koh Chang in Trat 212.404 km², so Samui is larger by more than 20 square kilometers. That makes Koh Chang the third-largest island in Thailand, after Phuket and Samui, even though many websites rank it second.
Which province has the most islands?
Phang Nga, with 155 islands, just ahead of Krabi with 154. In the Gulf of Thailand, Surat Thani has the most, with 108, including Koh Samui, Koh Phangan and Koh Tao. Chachoengsao has only one island.
Sources
- Department of Marine and Coastal Resources – Database of islands in Thailand (in Thai) (checked October 2026)
- Department of Marine and Coastal Resources – Diversity of Islands in Thailand, October 2008 (in Thai) (checked October 2026)
- Department of Marine and Coastal Resources – Islands infographic, 2018 (in Thai) (checked October 2026)
- Pollution Control Department, Region 13 – Islands in Thailand, citing DMCR (in Thai) (checked October 2026)