There are 8 *liquid* ounces in a cup. Dry ingredients are less dense than water, so a cup of any kind mix won't weigh 8 ounces. You just kind of have to figure out how much of the 8-oz bag you used, and work out the math from there. It's probably not going to be absolutely exact, but it's good enough for government work .

However, something else is not right here, because I don't see how there can be 10 servings of 4.5 ounces each in an 8-ounce bag. I think that 4.5 oz has to refer to the prepared pancakes, which is very non-helpful. Since you know there are 10 servings in the bag, take the serving info and multiply by 10, then divide by 8 to find out the nutrition per ounce. Look at how much of the bag was contained in a cup to find out how many ounces it was, and then use that to get the total counts.

Example: Let's say the bag lists a 4.5 oz serving as having 4g carbs. There are 10 servings in the bag, so 10 x 4 = 40g in the whole bag. The bag contains 8 oz, so each oz has 5g carbs. If a cup is half the bag, well, that's five servings to a cup. If your recipe makes 10 pancakes, then each of them will have 0.4 oz of mix, and will thus have 2g carbs (5g x 0.4) from the mix.

Can you tell I used to like those word problems?