The scientific unit of measure for the heat due to Capsaicin is based upon the Scoville Scale (parts per million).
The Scoville scale below defines the amount of heat for various peppers.
0-100 Scoville Units includes most Bell/Sweet pepper varieties.
500-1000 Scoville Units includes New Mexican peppers.
1,000-1,500 Scoville Units includes Espanola peppers.
1,000-2,000 Scoville Units includes Ancho & Pasilla peppers.
1,000-2,500 Scoville Units includes Cascabel & Cherry peppers.
2,500-5,000 Scoville Units includes Jalapeno & Mirasol peppers.
5,000-15,000 Scoville Units includes Serrano peppers.
15,000-30,000 Scoville Units includes de Arbol peppers.
30,000-50,000 Scoville Units includes Cayenne & Tabasco peppers.
50,000-100,000 Scoville Units includes Chiltepin peppers
100,000-200,000 Scoville Units includes Scotch Bonnet & Thai peppers.
200,000 to 300,000 Scoville Units includes Habanero peppers.
16,000,000 Scoville Units is Pure Capsaicin

Did you know... Capsaicin irritates the pain receptors on the tongue, not the taste buds. When your brain gets the signal from the pain receptors that something is happening in your mouth, it triggers the release of endorphins and other bodily chemicals that are intended to begin the healing process. When the endorphins reach the tongue and they discover that there is nothing going on they dissipate rapidly. The rush of endorphins causes you to feel a slight "high". It is this high that brings on your addiction to capsaicin and hot foods.

If you eat spicy hot foods on a frequent basis your body will build a tolerance to the pain and within a very short time you will be able to eat hotter and hotter foods. On a daily diet of spicy hot foods, one soon discovers that even our blazing hot dishes no longer give you the high you are expecting.