Many, if not all, growlers (1/2 gallon or 1 gallon) aren't designed to carb beer in. What you have right there is living proof. Sorry for the lost beer man. Happy no one was injured. Cheers!!!
i think it is usually measured by weight. but the amount of sugar is different for different sized bottles. i think you are supposed to use less priming sugar (per amount of beer) for bigger bottles