You can either use a food processor or if you don't have one (like me) just use a cheese grater.
Grate the bar of soap over a container in order to get 1 cup.
Here's what it looks like once grated.
Then add one cup of Broax and one cup of the Washing Soda.
Shake up the container to mix it and enjoy nice and clean laundry and a fraction of the price.
When washing clothes I use 2 tablespoons and when washing my cloth diapers I use only 1 tablespoon. When I grated up the soap the bar came out to be more than 1 cup so for this batch I'm leaving it this way but the next batch I'll add the whole bar. So far the detergent seems perfectly fine on the cloth diapers. I'll be sure to let you know if I notice leaking issues or smell issues on the diapers.