Why does my measuring cup give a different amount than the bag's cup?

First, physical cup sizes vary. A standard US cup is 8 fluid ounces, but not every household measuring cup is calibrated precisely to that, and some kitchen scoops are simply an approximate size rather than an exact standard.

Second, even with an identical cup size, different kibble shapes and densities pack differently, so the same volume can hold a different weight of food.

The safest approach is to ignore volume comparisons between your cup and the bag's chart altogether, and instead weigh out the gram amount your dog needs using a kitchen scale.

If you want to keep using a cup for convenience, weigh your own cup with your own food once, rather than trying to match it to what the bag describes.

Once you know your specific cup's gram weight for your specific food, write it down, since this removes the need to think about the mismatch again for as long as you use that food.

If you switch foods, repeat the process rather than assuming your previous cup's gram weight still applies. A quick note of each food's cup weight, kept somewhere you will actually see it, turns this from a repeated chore into a quick one off task for each new product you happen to try, and it only ever needs redoing when you change food again.