Most people probably weigh theirs before gutting. That's how I weighed the ones I've weighed.
Last year, I killed 75 or so hogs, and most were in the 100-200 pound range. I killed a few bigger, and weighed the biggest. The biggest tipped the scales at 275#, which blew my mind, because I thought he was much larger. I can lift a 200# mineral tub no problem, and myself and a friend couldn't come close to budging that hog.
I also used to guess weights based on what my show hogs used to weigh when they were around that same size. It would suprise you how much difference there is between a show hog and a wild hog that both look about the same size. The wild hog will weigh maybe 2/3 what the show hog weighs.