Granulated Onions are perfect when you are looking for desirable onion flavor, but you don't need the texture. Also ideal to use when time is of the essence, as the flavor is so good nobody but you will know the difference. Onion granules are easier to measure than Onion Flakes, and they don't cake like Onion Powder. Because of this, we like to use them in rubs and seasoning blends.
To rehydrate you can place them in a small bowl, cover the granules with water and let them sit for about 15 minutes, then drain off the excess water or you can mix with just enough cool water to make a smooth paste which can then be adding to the dish towards the end of cooking.
You can also substitute 1 Tablespoon of granulated onion for 1 /2 cup of fresh minced onion.
If you're looking to convert a recipe from fresh onions to dehydrated onions go with 1 small onion = 1 teaspoon onion powder or granulated onion = 1 tablespoon dried onion flakes.