Peppers are ranked by their level of concentrated capsaicin on the Scoville scale, ranging from the bell pepper on one end with zero Scoville Heat Units to the Carolina Reaper with 1,600,000 to 2,200,000 SHU.
A pharmacist named Wilbur Scoville developed the scale based on how much sugar water it would take to completely dilute the heat from a chile pepper. He had a group of people test how many cups of water they had to consume before their mouths no longer burned after consuming a pepper. Scientists no longer use this method, relying on the high-performance liquid chromatography test instead. Despite the more accurate method, they continue to convert their results into Scoville Heat Units.