Cayenne peppers have few true substitutions or alternative peppers, in ground, fresh or dried form, that come close to its ranking on the Scoville rating scale -- a numerical comparison of the spiciness in different varieties of chili peppers. Cayenne peppers have 30,000 to 50,000 Scoville heat units, or SHU, which puts them just above tabasco and serrano peppers.
Red chili powder matches cayenne pepper's color and heat the most closely. Red chili powder, made from the super red chili pepper, has 40,000 to 50,000 SHU and color ranging from fire-engine red to crimson. Paprika, made from chili peppers with 2,500 to 8,000 SHU, doesn't have nearly as much heat as cayenne pepper, but has a smoky aroma that gives the impression of a much hotter spice.
Dried and Fresh
Tabasco and de Arbol peppers are about the same size as cayenne peppers in their dried and fresh forms, and have comparable rankings on the Scoville scale: tabascos have 30,000 to 50,000 SHU and de Arbols have 15,000 to 30,000 SHU.