Thailand’s beaches are well established, with warm water and weather, good food, friendly relaxed people, comfortable accommodation and they’re cheap. Incredibly cheap compared to the Caribbean, Indian Ocean or the Pacific islands which are not dissimilar to Thailand though less crowded of course.
Thai beaches are frequently large, coated by soft white or beige sand, well serviced and in settings that are often strange but always comfortable, busy but relaxed.
For calmest waters choose the east side, Gulf of Thailand, though access is a little less convenient than the west coast as Phuket has an airport. The Gulf side exception is Koh Samui which has its own airport and is considering building another (which is a pretty good reason to avoid that island as it’s often uncomfortably busy).
The Bugcrew thought the brilliant white sand of Diamond beach (Sai Kaew) on Ko Samet on the east, Gulf side, was the finest of the many beaches in many regions that we wandered onto.
Note that while Phuket island takes the full force of storms (and tsunamis) coming off the Andaman sea, the island gives some protection to the Phi Phi islands and excellent protection to many Krabi beaches directly east tho not on the far east Gulf coast. See Thai Beaches Map
Ao Nang beach in the Krabi district on Thailand’s west coast, but crucially protected from Andaman Sea storms by Phuket island. Photo by Kallerna.
The Krabi province is coated with superb soft white sand and really stunning limestone scenery that tourists love to see and climbers love to ascend.
The two most famous beaches are West Railay (also known as West Rai Leh) and Phra Nang.
There are even more isolated powder sand beaches around Chicken Island that can be reached by longtail or kayak on day trips.
Krabi beaches offer a couple of interesting activity options including swimming at night in bio-luminescent waters, climbing the cliffs around Railay, sea kayaking among the incredible karsts and even a bit of hiking on a trail from East Rai Leh to Phra Nang.