How Does the Scoville Scale Work?
The Scoville Scale was created in 1912 by a man named Wilbur L. Scoville and was designed to measure the hotness from chili peppers or sauces derived from chilli peppers. Scientifically, the Scoville scale is used to measure the level of capsaicin found in a pepper. Capsaicin is the chemical compound that provides us as humans with the hot sensation. The Scoville test is done by diluting a pepper in sugar water.
Whatever the Scoville rating of a pepper, that is the ratio of how many times the pepper needs to be diluted before the heat sensation is no longer noticeable to the human tongue. An example

The following list contains chili peppers as well as a selection of popular brand name hot sauces accompanied by their Scoville rating.
Scoville Heat Units 16000000
16000000
16000000
9100000
8600000
7100000
5500000
5300000
4000000
2000000
1500000 - 2000000
1500000
1001304
1000000
1000000
923000
855,000 (reported)
800000
700000
600,000 - 900,000
600000
550000
500,000 - 750,000
400,000 - 500,000
357000
350,000 - 577,000
283000
250000
250000
234000
225000
225000
180000
175000
150000
125000
119700
100,000 - 350,000
100,000 - 325,000
100,000 - 225,000
100,000 - 200,000
100,000 - 125,000
95,000 - 110,000
90000
85,000 - 115,000
75,000 - 80,000
75000
50,000 - 100,000
50,000 - 100,000
49250
40,000 - 58,000
40,000 - 50,000
40,000 - 50,000
33390
30,000 - 49,999
30,000 - 50,000
30,000 - 50,000
15,000 - 30,000
15,000 - 29,999
12,000 - 30,000
11600
11000
8910
7,000 - 8,000
6,000 - 23,000
5790
5,000 - 10,000
5,000 - 10,000
3600
3400
2,500 - 8,000
2,500 - 5,000
2,500 - 5,000
2,500 - 5,000
2.085
2,000 - 2,500
1,200 - 1,800
1,500 - 2,500
1,000 - 2,000
1,000 - 2,000
1,000 - 2,000
1,200 - 1,800
747
700 - 1,000
600 - 800
500 - 2,500
500 - 1,000
450
400 - 700
100 - 600
100 - 500
100 - 500
0
Chilli Pepper / Hot Sauce
Pure capsaicin and Dihydrocapsaicin
Blair's 16 Million Reserve, from Gardner Resources, Inc.
Blair's 6 A.M., from Gardner Resources, Inc.
Nordihydrocapsaicin
Homodihydrocapsaicin and Homocapsaicin
The Source, from Original Juan Specialty Foods
Blair's 5 A.M., from Gardner Resources Inc. - No Longer available
Police grade Pepper spray
Blair's 4 A.M., from Gardner Resources Inc. - No Longer available
Common Pepper spray
Blair's 3 A.M., from Gardner Resources Inc.
Da' Bomb The Final Answer, from Original Juan Specialty Food
Naga-Bih Jolokia pepper
Cool Million Pepper Extract, from the Poison Pepper Co.
1 Million Scoville Pepper Extract, from Ashley Food Company, Inc.
The Dorset Naga Pepper, from Peppers by Post
The Naga Jolokia pepper (Capsicum frutescens), not confirmed
Satan's Blood, from Sauce Crafters Inc.
The Slap Heard Around the World, from Tiguana Flats
Blair's 2 A.M., from Gardner Resources, Inc.
Mad Dog 357 with Bullet Keychain, from Ashley Food Company
Blair's Mega Death Sauce, from Gardner Resources, Inc.
Dave's Insanity Private Reserve, from Dave's Gourmet (estimated)
Spontaneous Combustion Powder, from Southwest Specialty Foods Inc.
Mad Dog 357 Hot Sauce, from Ashley Food Company
Red Savina habanero (Capsicum chinense Jacquin)
Blair's Possible Side Effects, from Gardner Resources, Inc.
Vicious Viper, from CaJohns Fiery Foods
Dave's Ultimate Insanity Sauce, from Dave's Gourmet (estimated)
Da' Bomb Ground Zero, from Original Juan Specialty Foods
Not Cool Chocolate Habanero from Bahama Specialty Foods, Inc.
You Can't Handle This Hot Sauce, from Peppers
Dave's Insanity Sauce, from Dave's Gourmet (estimated)
Predator Great White Shark, from Peppers
Mad Dog Inferno Reserve, from Ashley Food Company
Crazy Jerry's Mustard Gas, from Crazy Jerry's, Inc.
Da' Bomb Beyond Insanity, from Original Juan Specialty Food
Habanero (Capsicum chinense Jacquin)
Scotch bonnet (Capsicum chinense)
Birds Eye pepper
Jamaican Hot pepper
Carolina Cayenne pepper
Bahamian pepper
Mad Dog Inferno, from Ashley Food Company
Tabiche pepper
Red Amazon Pepper
Chile-Today Red Amazon Powder, from Chile Today-Hot Tamale
Thai pepper (Capsicum annuum)
Chiltepin pepper
Blair's After Death Sauce, from Gardner Resources, Inc.
Piquin pepper
Super Chile pepper
Santaka pepper
Endorphin Rush Beyond Hot Sauce, from Garden Row Foods
Lottie's Original Barbados Red Hot, from Lottie's Island Flavours
Cayenne pepper (Capsicum baccatum and Capsicum frutescens)
Tabasco pepper (Capsicum frutescens)
de Arbol pepper
Lottie's Traditional Barbados Yellow, from Lottie's Island Flavours
Manzano pepper
El Yucateco XXXtra Hot Habanero, from El Yucateco
Crazy Jerry's Brain Damage, from Crazy Jerry's, Inc.
El Yucateco Green Chile Habanero, from El Yucateco
TABASCO ® brand Habanero Sauce
Serrano pepper
El Yucateco Red Chile Habanero, from El Yucateco
Hot Wax pepper
Chipotle, a Jalapeño pepper that has been smoked.
Cholula Hot Sauce, from Jalisco Food Company
El Yucateco Chipotle Hot Sauce, from El Yucateco
Santaka pepper
Jalapeño (Capsicum annuum)
Guajilla pepper
TABASCO ® brand Pepper Sauce
FRANK'S ® REDHOT ® XTRA Hot, from Reckitt Benckiser Inc.
TABASCO ® brand Chipotle Pepper Sauce, from McIlhenny Company
Tabasco Garlic sauce
Rocotilla pepper
Passila pepper
Ancho pepper
Poblano pepper
TABASCO ® brand Garlic Sauce
Texas Pete ®, from T.W. Garner Food Co.
Coronado pepper
TABASCO ® brand Green Pepper Sauce
Anaheim pepper
New Mexico pepper
FRANK'S ® REDHOT ® Original, from Reckitt Benckiser Inc.
Santa Fe Grande pepper
TABASCO ® brand SWEET & Spicy Pepper Sauce
Pepperoncini, pepper
Pimento
Sweet Bell pepper
Pure capsaicin and Dihydrocapsaicin
Blair's 16 Million Reserve, from Gardner Resources, Inc.
Blair's 6 A.M., from Gardner Resources, Inc.
Nordihydrocapsaicin
Homodihydrocapsaicin and Homocapsaicin
The Source, from Original Juan Specialty Foods
Blair's 5 A.M., from Gardner Resources Inc. - No Longer available
Police grade Pepper spray
Blair's 4 A.M., from Gardner Resources Inc. - No Longer available
Common Pepper spray
Blair's 3 A.M., from Gardner Resources Inc.
Da' Bomb The Final Answer, from Original Juan Specialty Food
Naga-Bih Jolokia pepper
Cool Million Pepper Extract, from the Poison Pepper Co.
1 Million Scoville Pepper Extract, from Ashley Food Company, Inc.
The Dorset Naga Pepper, from Peppers by Post
The Naga Jolokia pepper (Capsicum frutescens), not confirmed
Satan's Blood, from Sauce Crafters Inc.
The Slap Heard Around the World, from Tiguana Flats
Blair's 2 A.M., from Gardner Resources, Inc.
Mad Dog 357 with Bullet Keychain, from Ashley Food Company
Blair's Mega Death Sauce, from Gardner Resources, Inc.
Dave's Insanity Private Reserve, from Dave's Gourmet (estimated)
Spontaneous Combustion Powder, from Southwest Specialty Foods Inc.
Mad Dog 357 Hot Sauce, from Ashley Food Company
Red Savina habanero (Capsicum chinense Jacquin)
Blair's Possible Side Effects, from Gardner Resources, Inc.
Vicious Viper, from CaJohns Fiery Foods
Dave's Ultimate Insanity Sauce, from Dave's Gourmet (estimated)
Da' Bomb Ground Zero, from Original Juan Specialty Foods
Not Cool Chocolate Habanero from Bahama Specialty Foods, Inc.
You Can't Handle This Hot Sauce, from Peppers
Dave's Insanity Sauce, from Dave's Gourmet (estimated)
Predator Great White Shark, from Peppers
Mad Dog Inferno Reserve, from Ashley Food Company
Crazy Jerry's Mustard Gas, from Crazy Jerry's, Inc.
Da' Bomb Beyond Insanity, from Original Juan Specialty Food
Habanero (Capsicum chinense Jacquin)
Scotch bonnet (Capsicum chinense)
Birds Eye pepper
Jamaican Hot pepper
Carolina Cayenne pepper
Bahamian pepper
Mad Dog Inferno, from Ashley Food Company
Tabiche pepper
Red Amazon Pepper
Chile-Today Red Amazon Powder, from Chile Today-Hot Tamale
Thai pepper (Capsicum annuum)
Chiltepin pepper
Blair's After Death Sauce, from Gardner Resources, Inc.
Piquin pepper
Super Chile pepper
Santaka pepper
Endorphin Rush Beyond Hot Sauce, from Garden Row Foods
Lottie's Original Barbados Red Hot, from Lottie's Island Flavours
Cayenne pepper (Capsicum baccatum and Capsicum frutescens)
Tabasco pepper (Capsicum frutescens)
de Arbol pepper
Lottie's Traditional Barbados Yellow, from Lottie's Island Flavours
Manzano pepper
El Yucateco XXXtra Hot Habanero, from El Yucateco
Crazy Jerry's Brain Damage, from Crazy Jerry's, Inc.
El Yucateco Green Chile Habanero, from El Yucateco
TABASCO ® brand Habanero Sauce
Serrano pepper
El Yucateco Red Chile Habanero, from El Yucateco
Hot Wax pepper
Chipotle, a Jalapeño pepper that has been smoked.
Cholula Hot Sauce, from Jalisco Food Company
El Yucateco Chipotle Hot Sauce, from El Yucateco
Santaka pepper
Jalapeño (Capsicum annuum)
Guajilla pepper
TABASCO ® brand Pepper Sauce
FRANK'S ® REDHOT ® XTRA Hot, from Reckitt Benckiser Inc.
TABASCO ® brand Chipotle Pepper Sauce, from McIlhenny Company
Tabasco Garlic sauce
Rocotilla pepper
Passila pepper
Ancho pepper
Poblano pepper
TABASCO ® brand Garlic Sauce
Texas Pete ®, from T.W. Garner Food Co.
Coronado pepper
TABASCO ® brand Green Pepper Sauce
Anaheim pepper
New Mexico pepper
FRANK'S ® REDHOT ® Original, from Reckitt Benckiser Inc.
Santa Fe Grande pepper
TABASCO ® brand SWEET & Spicy Pepper Sauce
Pepperoncini, pepper
Pimento
Sweet Bell pepper