Confusing chili powder with cayenne pepper is potentially a worse culinary mishap than using baking powder in place of baking soda. In one case, your cake won't rise, but in the other, your dry rub might burn somebody's mouth off.
Cayenne pepper is not a chili powder substitute. Cayenne pepper is pure ground dried chiles, while chili powder is a blend of spices, of which cayenne happens to be but one.
The other ingredients include cumin, garlic powder, oregano, and paprika. But the ratio is one part cayenne to seven parts other things, depending on the blend (see below).
In other words, cayenne pepper is 8 times hotter than chili powder. If your recipe calls for two tablespoons of chili powder and you use two tablespoons of cayenne pepper instead — well, let's just say that you're unlikely to make that mistake twice.
Fortunately, you need not make it even once. Just remember that chili powder is a spice blend, whereas cayenne pepper is pure heat. If you want a mnemonic device, remember that the word cayenne has the letter Y in it, as in "why is my mouth on fire right now?" (No, it's not the most elegant mnemonic, but it'll work, which is what matters.)
If a recipe you're preparing calls for chili powder and you don't have any, the following mixture would be a great chili powder substitute:
Chili Powder Recipe
- 1 Tbsp ground cumin
- 2 tsp garlic powder
- 1 tsp cayenne pepper
- 1 tsp paprika
- 1 tsp ground oregano
Mix the ingredients together until well blended and you're ready to go. This will make a little less than 3 Tbsp of chili powder. Double it if you need more. Store in an airtight container.
Obviously, this recipe is only useful in the specific situation where you're out of chili powder but you have plenty of those other five ingredients.
Even so, it may be illuminating to see what chili powder is, what ingredients it's made up of, and in what proportions.
As you can see, the single most prominent ingredient is cumin. Together, the cumin and garlic powder make up fully half of the mixture. What you can conclude from that is that chili powder is not especially hot. Thus, chili powder alone is not going to be the primary source of heat in your chili or tacos. It's more like warmth.
Of course, if you make your own chili powder, you can make it as hot as you want. Bear in mind, however, that some recipes call for chili powder PLUS additional cayenne, so you might have to make some modifications.
Finally, some store-bought chili powders contain salt. But when it comes to salt, it's best to be able to control how much goes into a dish independently of the other seasonings. That's why there isn't any salt in the above blend. Season your dish with Kosher salt toward the end of cooking. And be sure to taste!