A chile pepper's heat is represented by the Scoville scale. The Scoville scale, measured in Scoville Heat Units (SHU), quantifies the pungency or heat of chili peppers and other spicy substances. It's based on the concentration of capsaicinoids, the compounds that cause the burning sensation, with higher SHU values indicating greater heat. A bell pepper, for example, has 0 SHU, while the Carolina Reaper, one of the hottest peppers, can reach over 2 million SHU.

Here's a breakdown of the scale:

• 0 SHU: Bell peppers, which contain no capsaicin.
• Mild: 100 to 2,500 SHU 🔥. Examples include the famous Hatch NM 6-4, Anaheim, and Pepperoncini. 
• Medium:  2,500 to 30,000 SHU 🔥🔥. Jalapeños and Serrano peppers fall into this range.
• Hot: 30,000 to 100,000 SHU 🔥🔥🔥. Cayenne and Thai peppers are examples.
• Extra Hot: 100,000 to 300,000 SHU 🔥🔥🔥🔥. Habaneros and Scotch Bonnets are in this category.
• Extremely Hot: Above 300,000 SHU 🔥🔥🔥🔥🔥. Ghost peppers, Morugas, Carolina Reapers and the new Pepper X are examples.

According to Wikipedia, the scale was developed by Wilbur Scoville in 1912, using a method called the Scoville organoleptic test, which involved diluting pepper extracts with sugar water until a panel of tasters could no longer detect the heat. Today, more accurate methods like High-Performance Liquid Chromatography (HPLC) are used to measure the concentration of capsaicinoids, the compounds that cause the burning sensation, and then converted to SHU.