A standard US cup holds exactly 8 fluid ounces for liquids, but dry ingredients are a completely different story.
For wet ingredients like water, milk, or broth, you can always count on 1 cup equaling 8 fluid ounces.
For dry ingredients, the weight in ounces depends entirely on the density of what you are measuring. For instance, a cup of fluffed all-purpose flour weighs about 4.25 ounces, while a cup of granulated sugar weighs closer to 7 ounces.