What does the average wedding cost? What is the average wedding size?

There is no "average" because there are a variety of factors, including the following:
~ geographic location (a New York City or another ‘big city’ wedding will be ALOT more than one in other areas)
~ meal (brunch or lunch will be less than a dinner)
~ type of food served ( a steak dinner will be more than a casual BBQ)
~ formality of event (more formal dinners will generally cost more)
~ who is making the food (caterers are more expensive than making the food yourself)
~ alcohol (no or limited is less expensive)
~ venue (different venues cost changes. Museums or historic homes will usually have a rental fee then you still have to pay for catering where as a reception-type place will usually not charge a rental fee but require you use their caterer)
~ dress (are you bargain-hunting or dropping $5k on a gown?)

I am in Central PA having a saturday wedding with 4-entree buffett and full open bar for 175 guests. I’m skrimping, clipping coupons, negotiating, and just cutting things out of the budget so we keep below $20,000 as our total budget. I’ve actually gotten down to about $18k and am hoping for more savings. Our reception venue is charging $52pp + tax & gratuity.

There are plenty of people whose family & friends just don’t add up to alot and they can invite everyone and still be under 100 people. There are just so many factors to this that there isn’t one answer.