European carriers publish their cabin allowance as a size and a weight, and the weight is what catches US travelers. Ryanair, Wizz Air and easyJet sell the overhead bag separately, while the flag carriers include it but cap it between 8 and 12 kg. A bag that flies free on Delta can cost money on the connecting leg to Lisbon.Every carrier here has its figures read off the airline’s own site and dated. Check the size checker before a trip that mixes a US airline with a European one, because the two rarely agree.