I really feel you on this, especially when you're planning your first trip with baby and want to get everything right. I don't have specific info on the Hamilton X1 or Z1 cabin dimensions off the top of my head, so I wouldn't want to give you the wrong details and cause stress at the airport lah. I'd suggest checking directly with the airline you're flying on, as each one has slightly different cabin baggage size limits, and also drop Hamilton a message to ask for the exact folded dimensions so you can compare.