To/From USA it is the per piece rule:
2 pieces: First piece: total dimensions not exceeding 62"/155 cm weight 70 lbs. (32 kgs). Second piece: total dimensions not exceeding 55"/138 cm weight 70 lbs.(32 kgs)
This is for economy (Tempo on AF) and will be more generous if you are in Business or first.
The fact you start in Germany and transit in Paris has no bearing, it is the fact you are travelling to the USA. If, however, you are stopping off in Paris, then they may enforce the 20Kg rule MUC-CGG.
If you have any doubts, please call AF.
[This message has been edited by LHR Tim (edited 06-13-2001).]