AIS, TrueMove and dtac cover Koh Samui, and your eSIM will use one of them. Thai mobile data is cheap and fast, and coverage around the island's ring road is good - our Bangkok and Phuket guides cover Thai networks, Grab and whether cafe wifi is enough. Samui's own peculiarities are two, and the first will cost you real money if you book without knowing it.
This is the single most useful piece of planning information about Koh Samui.
Bangkok Airways built and owns Samui airport, and it controls slot allocation there.
It is effectively the only network flying in. There is no budget competition on the direct route, and fares reflect that - a 65-minute hop from Bangkok commonly runs several thousand baht each way, and considerably more in peak weeks.
The alternative is the mainland. Fly a budget network - AirAsia, Nok Air, Thai Lion - to Surat Thani (URT) instead, then take the bus-and-ferry combination across.
It takes three and a half to four hours door to door rather than an hour, and it typically costs half to a third of the direct fare.
Combined tickets are sold at Surat Thani airport and online, covering the coach to the pier and the ferry to Nathon or Lipa Noi.
Which to choose: if you are travelling light, on a budget, or as a couple, the Surat Thani route is straightforwardly better value. If you are arriving late, with children or with a lot of luggage, pay for the direct flight and accept it.
Also consider Krabi or Phuket as entry points if you are combining coasts - the overland-and-ferry connections are well established.
A genuinely common and expensive confusion.
The Full Moon Party is on Koh Phangan, the island to the north, at Haad Rin beach.
Samui is the transport hub for it, which is why the two get conflated - most people fly into Samui and ferry across.
The ferry takes about 30 minutes from Bangrak or Big Buddha pier, and runs frequently.
Samui itself is not a party island in that sense. It is considerably more developed, more expensive and more oriented towards resorts, families and honeymooners than Phangan or Koh Tao.
Book accommodation on the right island. People do arrive on Samui expecting Haad Rin and find themselves an hour and a boat away from it.
Koh Tao, further north again, is the diving island - it is one of the cheapest places in the world to certify, and it is a different trip again.
Worth understanding, because Thailand's two coasts are on opposite schedules and travel advice frequently conflates them.
Samui sits on the Gulf of Thailand, not the Andaman Sea.
Its wet season is roughly October to December, peaking in November, when the northeast monsoon brings genuinely heavy rain and rough seas.
Phuket and Krabi are wettest from May to October, on the Andaman side.
So the coasts complement each other. June to September is often excellent on Samui while the west coast is soaked, which is exactly when many visitors avoid Thailand entirely.
November is the month to avoid here. Flooding is common, ferries cancel, and some beaches lose their sand temporarily.
January to April is the peak season - dry, hot and busy.
Ferries cancel in rough weather, which matters for the Phangan and Tao connections and for anyone with a flight to catch. Do not schedule an island hop the day you fly home.
The ring road and the developed beaches - Chaweng, Lamai, Bophut, Maenam - are well covered.
The interior is jungle and hills, and coverage thins on the tracks over the middle of the island. The waterfall roads and the viewpoints drop out.
On the ferries to Phangan and Tao, coverage comes and goes across the channel.
Ang Thong Marine Park, the archipelago northwest of the island and the landscape that inspired The Beach, has essentially nothing. Day trips there are a day offline.
Diving, obviously - and Sail Rock, between Samui and Tao, is the region's best-known site.
In heavy rain, service degrades and power cuts are not unusual on the island.
You need transport. Samui's ring road is about 50 km and the beaches are spread along it.
Songthaews - converted pickups - run fixed routes along the ring road cheaply. Agree the fare before boarding; they are not metered.
Taxis are notoriously expensive for Thailand and rarely use metres despite having them.
Grab operates, which removes the negotiation, and is generally the sensible choice. Our Phuket guide covers the ride-hailing situation in Thai resort areas more fully.
Scooters are everywhere and are the main cause of visitor injury. Thailand's road casualty rate is among the highest in the world, helmets are legally required and frequently ignored, and most travel insurance is void if you ride without a licence covering motorcycles. Rent one only if you genuinely ride.
Check your insurance wording before you get on a scooter. This is the single most common way a Thai beach holiday becomes a serious problem.
- Grab, for transport without the fare conversation.
- A ferry operator app or site - Lomprayah, Raja and Seatran run the crossings, and schedules change with the weather.
- Maps with offline copies for the island interior and Ang Thong.
- A weather app, particularly October to December.
- A translation app. English is widely spoken in the resort areas and thinner in the villages; Thai is tonal and not guessable.
Samui (USM) is a genuinely charming open-air airport with thatched pavilions and buggies instead of jetways, on the northeast of the island - and it is expensive to fly into, for the reason above.
Surat Thani (URT) plus ferry is the budget route, three and a half to four hours in total.
Ferries also run from Donsak pier on the mainland, and there are overnight train-and-ferry combinations from Bangkok that are slow, cheap and rather enjoyable.
Most nationalities enter Thailand visa-free for tourism for a period that has been extended in recent years - check the current allowance for your passport.
Modest. Resort and cafe wifi is good and widespread, the island is small, and Thai data is inexpensive. Where it earns its place is Grab, ferry schedules and weather - all of which you will check more often than you expect in the wet months.
Beach clothing, and something covering shoulders and knees for temples - Wat Phra Yai and the others enforce it.
Reef shoes for the rockier southern beaches.
A rain shell from October to December.
Modest cover off the beach. Thailand is relaxed but walking through a village in swimwear is poor form, and locals notice.
Serious sun protection - you are nine degrees off the equator.
Nothing formal, though the smarter resorts on Bophut and the north coast do dress for dinner.
Big Buddha (Wat Phra Yai), the 12-metre golden figure on its islet at the northeast corner, best in late afternoon.
Hin Ta and Hin Yai, the Grandfather and Grandmother rocks near Lamai, which are exactly what their names suggest and which Thai visitors find extremely funny.
Fisherman's Village at Bophut, the old Chinese-Thai shophouse street, on a Friday when the walking street runs.
Ang Thong Marine Park, the limestone archipelago with the hidden lagoon, on a day trip.
Na Muang waterfalls, in the interior.
The coconut plantations, which is what the island was before tourism and largely still is inland.
Silver Beach or Crystal Bay, the small coves between Chaweng and Lamai.
Sunset from the northwest coast at Maenam or Nathon.
Samui was a coconut island long before it was a resort, exporting millions of nuts a year to Bangkok, and the plantations still cover much of the interior.
The island had no roads at all until the 1970s. Crossing it meant a boat around the coast or a walk through the jungle.
Ang Thong Marine Park inspired the setting of The Beach, though the film itself was shot at Maya Bay in the Andaman.
Sail Rock, between Samui and Koh Tao, is one of the best-known dive sites in the Gulf, with a vertical chimney through the pinnacle.
The Gulf and Andaman coasts have opposite wet seasons, which is why Thailand has a good beach somewhere in almost every month of the year.
And Bangkok Airways calls itself Asia's boutique airline and owns three Thai airports, of which Samui is the one that most shapes a traveller's budget.
Songkran, in April, the Thai new year water festival, which on Samui is a several-day soaking.
Loy Krathong, in November, when floating offerings go out onto the sea.
The Full Moon Party, monthly, on Koh Phangan rather than here - see above.
January to April is the dry, peak season. June to September is the island's quiet secret, when the Andaman coast is wet and Samui often is not. October to December is the wet season, and November in particular is best avoided.
The love: Samui is the most comfortable of the Thai islands - excellent resorts across every price bracket, good food, an easy ring road, sheltered swimming on the northern beaches, and Phangan, Tao and Ang Thong all within a short ferry ride. It is a genuinely relaxing place, the infrastructure works, and the northern coast around Bophut and Maenam has kept a good deal of charm.
The complaints are consistent. Getting here is expensive unless you take the mainland route. Chaweng is overdeveloped and its beach road is a wall of bars, shops and traffic. Taxis are extortionate by Thai standards. The island is more expensive overall than Thailand's mainland or its cheaper islands. Scooter accidents injure a great many visitors every year. And people booking for the Full Moon Party regularly find they booked the wrong island.
Come between January and April or in June to September, fly to Surat Thani and take the ferry if the budget matters, stay on the north coast rather than Chaweng, and give Ang Thong a full day.
Because Bangkok Airways owns the airport and controls its slots, so there is effectively no competition on the direct route. The alternative is a budget flight to Surat Thani followed by a coach and ferry - three and a half to four hours in total, and typically half to a third of the price. Combined tickets are sold at the airport and online.
No - it is on Koh Phangan, at Haad Rin, about thirty minutes away by ferry. Samui is the transport hub for it, which is why the two get confused, and people regularly book the wrong island. Samui itself is a resort island rather than a party one.
October to December, peaking in November - which is the opposite of Phuket and the Andaman coast, where the wet months are May to October. That inversion is useful: June to September is often excellent on Samui while the west coast is soaked. Ferries cancel in rough weather, so never schedule an island hop the day you fly home.
Only if you genuinely ride and hold a licence that covers motorcycles. Thailand's road casualty rate is among the world's highest, and most travel insurance is void for unlicensed riders - which is how a cheap rental becomes an uninsured hospital bill. Grab and songthaews cover the island perfectly well.
