i would say 320. let me know if i win the prize.

If your plot it truly a 1/2 acre you planted far too few pumpkins. Typically you can expect around one pumpkin per vine which would put you at around 240, not all of which will be marketable.

Here is an article that I bet you'll wish you had a few months ago.

Clemson University Connecticut Field Pumpkin Study

Quick highlights are that their best results were with 605 plants per 1/2 acre (I scaled it to your plot) they grew 390 marketable pumpkins. Their worst results were with 151 plants per 1/2 acre that yeilded only 60 marketable pumpkins. Also keep in mind that they fertilized, and had a plan for pests and diseases. If you don't do any of those things it is likely your yeild would be lessened.

All that being said, you'll still have a lot of pumpkins if you tend your patch well. What is your experience with growing pumpkins?