Thai peppers are small, seldom growing larger than 1 to 3 inches (2.5–7.6cm) long. They are usually less than 1/2 inch (1.2cm) wide, but provide plenty of heat. These slightly curvy, potent peppers are typically bright red or deep green, and end in a sharp point.
Thai peppers are extremely hot, though they can vary in their heat ratings from 75,000 to 150,000 Scoville heat units. How high a chile pepper scores on the heat scale is determined by high-performance liquid chromatography measurement of how many parts per million of capsaicin it contains. (Capsaicin is the compound that gives chile peppers their fiery bite.) This figure is then converted into the historic Scoville heat units that signify how much dilution is necessary to drown out the chile’s heat. The heat level of a chile is given as a range because it varies with how and where the pepper was cultivated.