I think I will have to put this in bold letters. Just because it has the same prefix "baking" and both are leavening agents they cannot be used interchangeably, at least most of the time. There will be a noticeable difference in the taste and texture of the baked goods. Although I have seen comments in some of my recipes where the readers have mentioned that using one instead of the other has worked for them. Maybe they just got lucky. I have not tried it personally.
But theoretically speaking to substitute baking soda with baking powder, you may have to increase the quantity of baking powder at least 3 to 4 times to get the same amount of leavening and of course there will be a difference in the taste of texture. Similarly to substitute baking soda for baking powder you will have to increase the acidic ingredient in the recipe and reduce the quantity of baking soda by 3-4 times, which most probably will affect the taste and texture.
