From
https://www.lufthansa.com/online/por...373626#ancAbT8

Special baggage rules for travel to/from or across the USA

Under a consumer protection law issued by the US Department of Transportation, the following baggage rules apply to flights to/from or across the USA:



Consistent baggage rules apply to all parts of a journey to/from or across the USA. These include the free baggage allowance, the dimensions and weight of each of your bags, the level of any charges that may be incurred and hand luggage regulations.
The baggage rules set by the airline which is listed first on the ticket are those that usually apply here. If Lufthansa is listed on the first flight segment of your ticket, then Lufthansa’s baggage regulations will apply to your entire journey(1) — both your outbound and your return flight.
However, any airline which is listed as the first carrier on the ticket is at liberty to transfer the baggage rule stipulation to another airline in the itinerary (the so-called ‘Most Significant Carrier’). In such a case that other airline’s rules would then apply to the entire journey.
Lufthansa therefore cannot guarantee that, for a Lufthansa-issued ticket, the Lufthansa baggage rules will always apply in every case. Other airlines often have baggage rules which differ from those of Lufthansa.


For details of the free baggage allowance applying to your individual flight, please see your ticket and the e-mail confirmation which you receive from Lufthansa.