(select this link to see an updated report on pepper seed heat levels by the Chile Pepper Institute)
A pharmacist named Wilbur Scoville invented the Scoville Scale in 1912 to measure the heat of peppers. A "Scoville Unit" is actually a measure of capsaicin (the chemical in hot peppers that is responsible for their heat).
Scoville's test was a comparative taste test that is considered subjective by today's standards. A more sophisticated method is in use today, but in honor of Wilbur Scoville, the unit of measure is still called the Scoville.
The capsaicin level in peppers can vary from plant to plant due to local environmental conditions. This means that a pepper's rating is an average measure.
The hottest pepper on record is, depending where you read the latest 'hottest find', either the Naga Jolokia, Dorset Naga, or Bhut Jolokia. All are relatively recent finds with claims up to 1 million scoville units. By contrast, the Serrano Pepper comes in at about 5,000 to 15,000 Scoville units.
| Scoville Units | Pepper | Pepper | Pepper |
| 300,000 to 1,000,000 | Naga Jolokia | Dorset Naga | Bhut Jolokia |
| 100,000 to 300,000 | Habanero | Red Savina | |
| 50,000 to 100,000 | Chile tepin | Thai | |
| 30,000 to 50,000 | Tabasco | Pequin | Cayenne |
| 15,000 to 30,000 | De Arbol | ||
| 5,000 to 15,000 | Serrano | ||
| 2,500 to 5,000 | Guajillo | Jalapeno | Mirasol |
| 1,500 to 2,500 | Rocotillo | Cascabel | |
| 1,000 to 1,500 | Negro | Ancho | Pasilla |
| 500 to 1,000 | New Mexico | Anaheim | Mulato |
| 100 to 500 | Cherry | ||
| Zero | Bell | Pimento |