I am going to make this recipe today. I am using the simplers method. Just pick a measurement (one cup, one tablespoon, etc) and use that measurement to equal "1 part". In this case, the recipe calls for equal parts of all the ingredients. So, if one cup is your measurememnt you would use one cup of each of the ingredients.
Powdered castile soap (I use a block grader to powder one bar),
10-20 drops your favorite essential oil. Lavender works really well. So does grapefruit. I've been doing a combination of 10 drops rosemary and 10 drops sweet orange. The two fragrances work well together.
Use two heaping tablespoons for a medium wash and three for a large wash. I usually add extra borax if they load is really soiled. I am very pleased with the recipe. It is good for the environment, too.