What is the standard portion size (in ounces) that caterers go by?

For example, is it 4oz. of mostaccoli per person or 8oz.? What is the ratio or portion size I should use? I'm serving 8 different things, but want to make sure I have enough food.What is the standard portion size (in ounces) that caterers go by?
The standard is 4 ounces (half a cup) for sides and 4-6 ounces for main dishes. But I've seen caterers try to claim as small as 2 oz for the main dish. Rarely do you get to 8 oz or more, unless it's an inexpensive pasta dish.

It all depends on the capacity of the eaters. I've fed college students (12 oz wasn't enough) and senior lady luncheons (4 oz. made a lot of leftovers).What is the standard portion size (in ounces) that caterers go by?
when i had my wedding we found most allotted 4oz each. my husbands family are big eaters so we went with a italian family style buffet with 8oz per person. we had 4 no shows and had no leftovers. oh yea had 4 main dishes salad and 4 sides, and cake.