This is the recipe I use for making laundry soap:
Grate 1 bar of Dr. Bronners bar soap (I've also seen the recommendations to use Ivory soap or Fels Naptha soap, but I like Dr. Bronners, and as a bonus, it smells yummy when you use the peppermint LOL. Ivory would be the cheapest & easiest to find though). Now just mix equal parts of the grated soap, washing soda (this is not baking soda, but it's in a box that looks like a big baking soda box, the typical arm & hammer box, on the laundry aisle), and borax (also in the laundry aisle). Mix them all together, put them in a container w/ a lid, and use about 1/8 c per load of laundry.