I need to substitute butter for a half a cup of shortning in a recipie. How much butter should I use?

Use the same amount of butter as you would have used with the shortging.

Half a cup of butter - 1 stick. Because you always have a choice; butter, margarine, shortening are all fats. Except if you were to substitute butter or margarine with shortening you have to include water with the shortening.

Well your question is confusing though.

If you want to substitute butter for shortening - then it would be a half a cup of shortening and 3 teaspoons water.

If you want to substitute shortening for butter - then it would be a half cup of butter.

Yes but keep in mind that butter has water in it that shortening doesn't have so you also need to modify the liquids. For every cup of butter there are 6 teaspoons of liquid that shortening does not have. Now this is butter, if you really mean margarine, I assume it doesn't have liquid, but I really don't know, I don't use margarine.

Umn - half a cup. Which I believe is 1 stick.

should be the same amount