One clove of garlic is the equivalent of 1 teaspoon of chopped garlic. It is also equal to 1/2 teaspoon of minced garlic and 1/8 teaspoon of dried garlic powder.
Other substitutions include 1/4 teaspoon of granulated garlic or 1/2 teaspoon of garlic juice. Shallots, elephant garlic or onion can also be used in place of garlic.
While garlic powder does not have the body of fresh garlic, it does provide a strong flavor. Fresh garlic is more pungent, but it does not mix as well into soups. Garlic juice is usually found in the produce section; it can be sprayed on or poured into dishes.