Vanilla extract vs. Vanilla powder What is the difference among the vanilla extract and the powdered vanilla?

When I'm making a certain recipe if it required vanilla extract, is it ok to replace it with powder, and what is the proportion among them?

I am intending to use powdered vanilla in a buttercream recipe from Martha Stewart's recipes, is it recommended to substitute?
My best experience is that you should use 1/4 teaspoon of the vanillin powder for each teaspoon of vanilla extract.

I use it for bread dough, donut dough, but never for icing.