Thailand's Islands: Which One, and When

Thailand’s islands sit in two different seas on opposite calendars, and that single fact decides more about a beach trip than any ranking of the ten prettiest can. The Andaman coast in the west and the Gulf in the east are not two flavours of the same holiday. They are wet at different times, calm at different times, and reached by different airports.

So this page does not open with a list. It opens with the measurement, because “the best island in Thailand” is a question with a different answer in January than in July, and the difference is large enough to ruin a fortnight.

Eight islands, twelve months

Four things worth taking from that table.

The coasts invert, and it is not subtle. From May to August not one of the four Andaman islands is dry, and all three of the Gulf ones are. In July, Koh Samui takes 90mm and Phuket takes 223mm. That run is exactly when the northern hemisphere takes its summer holiday, which is why so many people come home from a Thai beach having spent it indoors: they booked the famous coast in the wrong month.

The Gulf is dry for more than twice as many months. Koh Samui, Koh Phangan and Koh Tao each manage nine months under 150mm. Phuket, Koh Lanta and Koh Lipe manage four. The Andaman’s reputation is built on the four months it is spectacular, and it is genuinely spectacular in them.

October is the month with no answer. It is the only one in the table where not a single island of the eight is dry: the Andaman is at its annual wettest, the Gulf’s own late rainy season has just begun, and for a few weeks there is nowhere on this coast or that one to move to. If your dates are fixed in October, plan a trip that is not principally about a beach.

Rain and sea do not agree. Several of these islands are at their calmest in a month they are also at their wettest, Koh Samui most sharply: its flattest sea of the year is in October, at 0.24 metres, in its second-wettest month. A page that shows only one of the two numbers is hiding the trade rather than making it.

Pick the coast, then the island

The Andaman coast, in the west

This is the postcard: limestone karst rising vertically out of the water, hidden lagoons, and water that goes an implausible green. Phuket is the gateway and the only island here with a full international airport. Krabi on the mainland opposite is the launch point for Railay and the Phi Phi group.

Koh Phi Phi is the famous one and the busiest small island in the country, with the best water and the least peace. Koh Lanta is its opposite: long, flat, quiet, and about ninety minutes from Krabi. Koh Lipe is four hundred kilometres further south, near the Malaysian border, which is why it has its own weather in the table above rather than sharing Krabi’s.

Season: November to March, and April on the outer islands. The whole coast is on our Andaman coast guide.

The Gulf, in the east

Lower, greener and rounder: granite boulders and coconut palm rather than vertical limestone, and a sea that is calmer in most months. Koh Samui is the anchor and has its own airport, an expensive one. Koh Phangan next door is far more than the full moon party it is known for, and Koh Tao beyond it is small, steep, and the cheapest place in Asia to learn to dive.

The three sit close enough to combine on one trip without a flight, which is the practical argument for this coast and is not true of the Andaman. The region is on our Gulf islands guide.

Season: January to August, with the wet arriving in late October and November, which is the opposite of the Andaman and the thing most trip plans get wrong.

The eastern seaboard, near Bangkok

Koh Samet belongs to neither. It is three hours from Bangkok by road and boat rather than by flight, it is inside a national park, and it runs on its own calendar: December is its driest month at 12mm, the lowest single figure of any island in the table. It is a weekend island rather than a holiday island, and it is the right answer to a spare two days at the end of a trip.

How many islands does Thailand have

Nobody can tell you, and we are not going to pretend otherwise.

The number repeated across travel pages is 1,430, and we could not trace it to a primary source. A figure of 936 is widely attributed to Thailand’s marine and coastal resources department, and we could not verify that directly either. Both are quoted with total confidence by sites that have not checked them.

The reason the number is soft is that it depends entirely on how small a rock still counts as an island, and nobody publishing a total says which rule they used. What is checkable is the scale of single clusters: Phang Nga Bay alone holds dozens, and so do the archipelago national parks at Ang Thong, Tarutao and Koh Chang.

The practically useful answer is a much smaller number. Around a dozen Thai islands have the airport, the boats, the accommodation and the food to build a holiday on, and eight of them are in the table above.

Is Thailand an island

No, and it is asked often enough to answer plainly. Thailand is a mainland country in Southeast Asia with land borders on Myanmar, Laos, Cambodia and Malaysia, and roughly 3,200 kilometres of coastline on two separate seas. The islands are offshore, and they are what most visitors come for, but the country is not one of them.

Island hopping, and what it actually costs

Hopping works within a coast and stops working across them.

Within a coast the boats are frequent, short and cheap. Phuket to Phi Phi is a couple of hours; Samui, Phangan and Tao are a chain of short ferry legs. Our route pages carry the real timings for the crossings we have checked.

Across the coasts is a different proposition. The Andaman and the Gulf are on opposite sides of a peninsula, so getting from Koh Lanta to Koh Tao means an internal flight, or the best part of a day of minibus, bus and boat. It is done, and it is usually done by people who did not realise how far apart they were when they booked.

How many islands in two weeks? Two, or three at the outside, on one coast. Every move costs a half day at each end once you have counted the checkout, the boat, the transfer and the business of finding your feet. A fourth island buys you a travel day rather than a beach day.

What this page does not do

It does not rank the beaches. That page exists, it measures 37 of them individually by wave height, and it is the better tool once you have chosen an island.

It does not tell you the best time to visit Thailand as a country, which takes the north and Bangkok into account as well as the coasts: the month-by-month guide does that.

And it does not yet have a page of its own for Koh Phi Phi, Koh Lanta or Koh Lipe. They are measured here because the data existed and the table would have been dishonest without them, and the guides are not written. We would rather say so than imply otherwise.