50,000 - 100,000 Scovilles.
Despite the common belief, there is no single "Thai chili pepper" though most candidates for the title are small in size and high in heat or pungency. There are at least 79 separate varieties of chili that have appeared from three species in Thailand. While the names of chili peppers are often "hotly" debated and therefore in a volatile state of flux the world over, some would say that there is particular confusion when the subject comes around to Thai peppers.
Prik num or "banana peppers," for instance, also resemble a New Mexican pepper, and they are also grown in Kashmir, India, and thus are also known as Kashmir peppers. Further confusion arises because the Kashmir is ALSO known as the Sriracha, a name associated with the famous sauce originally made from these peppers in the Thai seaside town of the same name.
Oddly, the peppers now featuring in the sauce known around the world as Sriracha are red Serrano peppers! At least in agricultural terms, we specify that two types of chili peppers grow for harvest in Thailand: the prik khee nu or "bird pepper" and the prik khee fah or plain "chili pepper."
Whatever the case regarding names, Thai chili peppers usually turn up ground from fresh to add heat to curry pastes for very spicy dishes and for very colorful dishes at the same time - the traditional Thai cook being as interested in presentation as the traditional Japanese cook, for instance, and therefore garnishing hot dishes with a pleasing array of hot peppers.
Thai chili peppers also appear in other Asian cuisine including that of Myanmar, where they are known as nga yut thee, frequently featuring in curries, as well as in balachuang, a spicy relish never absent from any meal. Laotian cuisine utilizes similar peppers and calls them mak phet; they appear in pastes and even end up stuffed and steamed to create spicy vegetable and fish dishes.
Related peppers are also known to be favored in Cambodia, and are widespread in Vietnam where they enliven pastes and sauces, especially those with local fish flavors, of course.