Can you use cocoa powder instead of baking chocolate?

actually I've heard it is probably best you do not substitute and liquid for a powder because it can turn baked stuff super moist when baking but if you were trying to make a cup of chocolate milk or something like that you would use 1/2 cup sugar and 1/2 cup of cocoa powder for chocolate milk but if you are just trying to substitute the two you can't because one is a liquid and the other is not the same consistency hope i helped! good luck!