In my experience all Gold/Silver coinage is expressed in Troy. The gold eagles contain 1 troy oz of gold plus a little silver and copper. That is why it weighs 1.0909 troy oz's.
http://en.wikipedia.org/wiki/American_Gold_Eagle
Krug's have a darker gold color (more orange) because of there higher copper content but still contain 1 troy oz of Au but weigh a bit more then 1 troy oz. The Canadian maples are .999 gold and weigh almost exactly 1 troy oz.
I have a grain scale and have played with these and found them to really close to there stated weights.
Try this site to do the conversions: http://www.convert-me.com/en/convert/weight