I have an app on my phone called 'convert units' and it saves me from many conversion catastrophes!

I always go by 1 C. = 8 oz.

FYI, typically containers tell you how many servings and what the serving size is, so you can usually figure it out. For example, if the serving size is 2 T and there are 8 servings in a container, then the container holds 1 cup (16 T per cup.)

4 oz, half your container, half a cup.