thumb|upright=1.4|Pepper stand at [[Central Market (Texas)|Central Market in Houston, Texas, showing its peppers ranked on the Scoville scale]]
thumb|The [[ghost pepper of Northeast India is considered to be a "very hot" pepper, at about 1 million SHU.]]
thumb|The [[Naga Morich, with around 1 million SHU, is primarily grown in India and Bangladesh.]]
The Scoville scale is a measurement of spiciness of chili peppers and other substances, recorded in Scoville heat units (SHU). It is based on the concentration of capsaicinoids, among which capsaicin is the predominant component.
The scale is named after its creator, American pharmacist Wilbur Scoville, whose 1912 method is known as the Scoville organoleptic test. The Scoville organoleptic test is a subjective assessment derived from the capsaicinoid sensitivity by people experienced with eating hot chilis.
Scoville organoleptic test
In the Scoville organoleptic test, an exact weight of dried pepper is dissolved in alcohol to extract the heat components (capsaicinoids), then diluted in a solution of sugar water.
A weakness of the Scoville organoleptic test is its imprecision due to human subjectivity, depending on the taster's palate and number of mouth heat receptors, which vary widely among subjects.
Quantification by HPLC
thumb|The [[Red Savina pepper, a hot chili]]
Since the 1980s, spice heat has been assessed quantitatively by high-performance liquid chromatography (HPLC), which measures the concentration of heat-producing capsaicinoids, typically with capsaicin content as the main measure. For law-enforcement-grade pepper spray, values from 500,000 up to 5 million SHU have been reported, but the actual strength of the spray depends on the dilution.
Numerical results for any specimen vary depending on its cultivation conditions and the uncertainty of the laboratory methods used to assess the capsaicinoid content.
{| class="wikitable"
|-
! Scoville heat units <!--Dragons Breath, Apollo pepper, and Chocolate 7-pot have not been officially verified; add only peppers with a reliable source for its Scoville score; this table does not display a comprehensive list-->
! Examples
|-
| style="color:white; background:#600; text-align:right; padding-right:8px;"| 2,693,000 || Pepper X
|-
| style="color:white; background:#800; text-align:right; padding-right:8px;"| 1,500,000–2,500,000 || Carolina Reaper
|-
| style="color:white; background:#900; text-align:right; padding-right:8px;"| 750,000–1,500,000 || Trinidad Moruga scorpion, Naga Viper pepper, Infinity chili, Ghost pepper
|-
| style="color:white; background:#c00; text-align:right; padding-right:8px;"| 350,000–750,000 || Red savina habanero
|-
| style="color:white; background:#f00; text-align:right; padding-right:8px;"| 100,000–350,000 || Habanero chili, Scotch bonnet pepper,
|-
| style="color:white; background:#ff2424; text-align:right; padding-right:8px;"| 50,000–100,000 || Bird's eye chili (Thai chili pepper), Malagueta pepper Cayenne pepper
|-
| style="background:#ff6d6d; text-align:right; padding-right:8px;"| 10,000–25,000 || Serrano pepper, Aleppo pepper, Cheongyang chili pepper
|-
| style="background:#ff9292; text-align:right; padding-right:8px;"| 2,500–10,000 || Jalapeño pepper, Guajillo chili
|-
| style="background:#ffb6b6; text-align:right; padding-right:8px;"| 1,000–2,500 ||Poblano pepper
|-
| style="background:#ffdbdb; text-align:right; padding-right:8px;"| 500–1,000 || Cubanelle,
|-
| style="background:#fee; text-align:right; padding-right:8px;"| 0–500 || Banana pepper, Friggitello, Pimiento
|-
| style="background:#fff; text-align:right; padding-right:8px;"| 0 || Bell pepper, Peperone crusco
|}
thumb|The capsaicin "[[pharmacophore", the portion of the molecule that produces biological effects]]
The class of compounds causing pungency in plants such as chili peppers is called capsaicinoids, which display a linear correlation between concentration and Scoville scale, and may vary in content during ripening. Capsaicin is the major capsaicinoid in chili peppers. In the table below, non-capsaicinoid compounds are italicized. The ratings for piperine (150,000 SHU) and gingerol (60,000 SHU) for example are comparative estimates and are not official Scoville ratings. While the ratings are expressed in Scoville Heat Units (SHU), they do not technically belong on the official Scoville scale because the scale is scientifically designed and defined exclusively for capsaicinoids found in chili peppers.
{| class="wikitable"
|-
! Scoville heat units
! Chemical
|-
| style="color:white; background:#000; text-align:right; padding-right:8px;"| 16,000,000,000
| Resiniferatoxin
|-
| style="color:white; background:#000; text-align:right; padding-right:8px;"| 5,300,000,000
| Tinyatoxin
|-
| style="color:white; background:#300; text-align:right; padding-right:8px;"| 16,000,000
| Capsaicin
|-
| style="color:white; background:#300; text-align:right; padding-right:8px;"| 15,000,000
| Dihydrocapsaicin
|-
| style="color:white; background:#ff1515; text-align:right; padding-right:8px;"| 150,000
| Piperine
|-
| style="color:white; background:#ff1515; text-align:right; padding-right:8px;"| 60,000
| Gingerol