A single clove of garlic is equal to 1/2 teaspoon of minced garlic, which is the same as 1 teaspoon of chopped garlic. If the cook only has dry garlic, she should use 1/8 teaspoon of garlic powder or 1/4 teaspoon of granulated garlic.
Dried spices are more condensed and have a stronger flavor, which is why a cook uses less of them in a substitution. A cook may make other substitutions as well, such as using garlic juice. Garlic juice is usually stocked in the spice section. The cook may also use minced shallots, green onions, elephant garlic, garlic greens or onions in place of the minced garlic.