The Scoville scale measures the heat of chilli peppers in Scoville Heat Units (SHU). A bell pepper scores 0, a jalapeño a few thousand, a habanero hundreds of thousands, and today’s record holder, Pepper X, more than 2.6 million.
Wilbur Scoville and his test (1912)
American pharmacist Wilbur L. Scoville worked in the laboratory of Parke, Davis & Co. in Detroit. In 1912, in a short paper titled “Note on Capsicums”, he described a simple test: one grain (about 65 mg) of ground capsicum is macerated overnight in 100 ml of alcohol and filtered; the solution is then added to sweetened water in definite proportions “until a distinct but weak pungency is perceptible on the tongue”. The result is a dilution – how many times the extract has to be diluted until the heat almost disappears.
Scoville measured, for example, Japan chillies at 1:20,000–30,000, Zanzibar chillies at 1:40,000–45,000 and Mombasa chillies at 1:50,000–100,000. Even then he noticed that pungency varies with growing conditions.
The method later became a standard sensory test in which the solution is diluted until a panel of trained tasters can no longer detect the heat. Its weakness is subjectivity: people tolerate heat differently, tasters become desensitised, and results from different laboratories can vary considerably.
Measuring heat today: HPLC
Today heat is measured instrumentally by high-performance liquid chromatography (HPLC). The laboratory measures the individual capsaicinoids – the compounds responsible for the burn – and converts them to SHU. Under ASTA Method 21.3 (based on AOAC 995.03), total heat is the sum of three compounds: capsaicin and dihydrocapsaicin are multiplied by a factor of 16 million, nordihydrocapsaicin by 9.3 million. Pure capsaicin therefore rates 16,000,000 SHU.
The conversion from ppm of capsaicinoids to SHU is not uniform: authors use factors from 15 to 16.1, so figures from different labs are not always directly comparable. The Guinness records (Carolina Reaper, Pepper X) were measured by HPLC.
Heat table
Values from the University of Florida (UF/IFAS); other universities give slightly different ranges, and heat varies with cultivar and growing conditions.
| Pepper | SHU |
|---|---|
| Bell pepper | 0 |
| Cubanelle | about 1,000 |
| Poblano | 1,000–2,000 |
| Anaheim | 1,000–5,000 |
| Jalapeño | 2,000–8,000 |
| Serrano | 10,000–25,000 |
| Cayenne | 25,000–50,000 |
| Tabasco | 30,000–50,000 |
| Thai chilli | 50,000–100,000 |
| Habanero, Scotch bonnet | 100,000–350,000 |
| Bhut Jolokia | 1,041,427 |
| Trinidad Moruga Scorpion | mean 1,207,764 (NMSU 2012) |
| Carolina Reaper | 1,569,300 (Guinness 2013) |
| Pepper X | 2,693,000 (Guinness 2023) |
| Pepper spray | 2,000,000–5,300,000 |
| Pure capsaicin | 16,000,000 |
The heat of a single variety changes with growing conditions – something Scoville himself noted in 1912.
Why chilli burns
Capsaicin binds to the TRPV1 receptor in nerve endings. The same receptor responds to painful heat, which is why chilli feels “hot”. More in History of chilli.
Sources
- Scoville W. L. (1912): Note on Capsicums. Journal of the American Pharmaceutical Association 1(5): 453–454. doi:10.1002/jps.3080010520, PDF
- NIST: How do you measure the heat of a pepper?
- ASTA: Method 21.3 (2026) – Pungency of Capsicums and Their Oleoresins (HPLC)
- Hayward, Leaver, Crampton (2026): systematic review of pungency measurement. Food Science & Nutrition 14(1): e71407. PMC12835616
- Collins M. D., Wasmund L. M., Bosland P. W. (1995): Improved method for quantifying capsaicinoids in Capsicum using HPLC. HortScience 30(1): 137–139. doi:10.21273/HORTSCI.30.1.137
- UF/IFAS Gardening Solutions: Peppers by Scoville units
- University of Arizona Extension: Peppers (Chiles)
- Scientific American: About pepper spray (2011)
- Bosland P. W., Coon D., Reeves G. (2012). HortTechnology 22(4): 534–538. doi:10.21273/HORTTECH.22.4.534
- Guinness World Records: Pepper X (2023)