How big is a marmot?

I've seen some pretty big marmots, usually not any longer than 20 inches, but much fatter than the one pictured here. Of course, I've also encountered smaller, more slender marmots.

If you want to see really fat marmots, go out hiking up in the high elevation meadows of the Cascades in mid September. This is right before marmots climb in their burrows to hibernate, so they are spending alot of time eating and getting fat. I've also noticed that marmots seem to be more accepting or ignorant of human presence during this time of year.