This is what my daughter and I both use. We use 2 small containers and add a scoop from each container.
Grate a bar of Fels Naptha, Zote or Ivory Soap. Put in a container.
In second container, mix equal amounts of Arm and Hammer washing Soda and Borax.
Use one scoop from each container and you're good to go.
We use scoops like the size that come in Koolaid.
We originally mixed the soap with the powders, but found it hard to get equal amounts in the scooper. Then at the bottom of the batch, it was mostly soap and little powder.
Works really well....but don't be looking for suds in your washer! lol
Carol B