How full is that keg?

Any moderately serious home brewer ends up going the kegging route after a few too many sessions of bottle washing, and inevitably, the first kegging experience ends in disappointment -- not because the beer is bad, but because the keg runs out sooner than you could imagine. A keg has about 50 beers in it, and in your early home-brewing excitement, you tend to invite 10 or so beer-loving friends over a few nights a week. The math doesn't look good. The next thing you know, the brew is all gone and you hear the collective groans of your friends as the last vestiges of foam sputter out of your keg. It's an ugly sound -- I've been there.

Kevin Railsback points to a site with a method to figure this out ahead of time. You won't prevent the inevitable disappointment, but at least you'll have some advance warning.