Scoville's original method for testing hotness was called the Scoville Organoleptic Test, which he developed in 1912. As originally devised, a solution of the pepper extract is diluted in sugar water until the "heat" is no longer detectable to a panel of (usually five) tasters; the degree of dilution gives its measure on the Scoville scale. Thus a sweet pepper, containing no capsaicin at all, has a Scoville rating of zero, meaning no heat detectable even undiluted. Conversely, the hottest chiles, such as habaneros, have a rating of 300,000 or more, indicating that their extract has to be diluted 300,000-fold before the capsaicin present is undetectable. The greatest weakness of the Scoville Organoleptic Test is its imprecision, because it relies on human subjectivity. Being a natural product, the heat can vary from pepper to pepper, so this scale is just a guide.

HotSauce.com Scoville Chile Flame Scale
Pepper & Extract Varieties	Flame Rating	Scoville Heat Units (SHU)
Sweet Bell Peppers, Sweet Banana, Pimento		0 - 100
Mexican Bell, Cherry; New Mexico, Anaheim, Pepperoncini		100 - 1,000
Ancho, Pasilla, Espanola, Anaheim		1,000 - 1,500
Sandia, Cascabel, NuMex Big Jim		1,500 - 2,500
Jalapeno, Mirasol, Chipotle, Poblano		2,500 - 5,000
Yellow Wax, Serrano		5,000 - 15,000
Chile de Arbol, Manzano		15,000 - 30,000
Aji, Cayenne, Tabasco, Piquin		30,000 - 50,000
Santaka, Chiltecpin, Thai		50,000 - 100,000
Habanero, Scotch Bonnet, Bird's Eye, Jamaican Hot		100,000 - 350,000
Red Savina Habanero, Indian Tezpur		350,000 - 855,000
Dorset Naga		876,000 - 970,000
Naga Jolokia Pepper ("Ghost" Pepper)		855,000 - 1,041,427
Common Pepper Spray		1,150,000 - 2,000,000
US Grade Police Pepper Spray		2,500,000 - 5,300,000
Homodihydrocapsaicin		6,000,000 - 8,600,000
Nordihydrocapsaicin		8,800,000 - 9,100,000
Pepper Extracts, Blair's Reserve's, The Source, Dave's Private Reserve		2,000,000 - 10,000,000
Pure Capsaicin, Blair's 16 Million		15,000,000 - 16,000,000