The amount of substitute you should use depends on the recipe and your personal taste preferences. As a general rule, use approximately half the amount of onion salt or fresh onions as you would onion powder. For dried minced onions or onion flakes, use equal amounts. For shallots, use approximately 1 tablespoon of minced shallots per teaspoon of onion powder. And for garlic powder, use half the amount as you would onion powder.