1 cup grated Fels Naptha Soap (I use the fine side of a hand grater for this to be sure the soap fully dissolves)1/2 cup washing soda
1/2 cup 20 mule team borax
Mix together and store in a container. Use 2 Tablespoons per load. A lot of powdered drinks come with a 2 T. scoop that you could use.
I do not use the powdered detergent very often because it is not as cost effective as the liquid, but it is great for camping or traveling when you don’t want to have to lug a big bottle of detergent along. I have never used any other soap than the fels-naptha for this (I bought a case), but you could always try it with castille or Ivory soap.