Originally Posted by CAlex

The rules say that you are allowed a 55+40+20cm piece of luggage, plus a computer bag. I travelled a lot with LH in Europe last year and I always had one 55+40+20cm bag with clothes for a week (usually ~11-13kg), plus a computer bag (sometimes quite large due to accessories), weighting ~5-7kg. It was weighted most of the times, when I checked-in. For online check-in, nobody even minded it, and it was never the largest piece of luggage on the flight.

I do not know the difference between the "american standard" and "other standards", but if the OP had indeed a bag as described, it seems like the gate agent was beyond strict.

If the luggage was never measured or weighted, then I would file a written complaint with Lufthansa and ask for compensation. Words of frustration would not help outside this forum, you should keep it strictly factual.