[Daylene Alford]

76oz box = 9.5 cups
55 oz box = 6.875 cups

This calculation is incorrect because the 55oz of washing soda is dry weight while cups are fluid measures. In order to get the correct measurement you must weight a cup of washing soda which I did. One cup of washing soda is 9.8 oz (yes, I did zero the scale with the weight of the cup before adding the soda). This may vary a quite a bit depending on the density of the soda and/or variations in measuring utensils. For example one of my cup measures is larger then all the others. This means that a 55oz box of washing soda has about 5.6 cups not 6.875.

Now borax only weights 6oz for 1cup so in a 76oz box you get 12.67 cups.

I know this post is old but it showed up as a first result when I googled this so I thought I would go ahead and post so people aren't finding incorrect information.