In a nutshell, no, you can't substitute baking powder for baking soda. Baking soda is four times as strong as baking powder — so if your recipe calls for 1 teaspoon of baking soda, you would need four teaspoons of baking powder to produce the same amount of lift. Unfortunately, though, it’s not that simple. Baking powder is made of baking soda and the right amount of acid to react with the soda (it also includes corn starch to keep the ingredients from prematurely reacting in the privacy of their container). So if your recipe already has acidic ingredients that were going to neutralize the necessary baking soda, you are adding other ingredients in the baking powder that may not sit well with them. On the other hand, substituting for a lack of baking powder is very easy: 1/4 teaspoon of baking soda plus 1/2 teaspoon cream of tartar (ignoring the cornstarch) for each teaspoon of baking powder required.