Star Alliance is the largest of the three global alliances, and membership matters for your bags in one specific way: elite status earned on one member, Star Alliance Gold, buys an extra checked bag or extra weight on every other member. It does not harmonize the allowances themselves. United publishes a box size and no cabin weight, Lufthansa caps the cabin bag at 8 kg, and Singapore Airlines weighs it at 7 kg.On a connecting ticket across two members, the most significant carrier rule decides whose allowance applies for the whole journey. Each carrier page below shows the figures read off that airline’s own site and the date they were checked.