Smash cut to 2014 and my wife and I are preparing for an extended trip through Europe. Since we planned to live out of a bag for many months, the decision of which luggage to choose was very daunting. We wanted something that was spacious, comfortable, durable, and (above all) fit all the carry-on limits for the airlines we planned to fly on.
This is the website I wish I had when planning for that trip.
Airlines have limits on the size of luggage they deem "acceptable" to fit in the cabin of their airplanes. Even though they are explicit about these numbers, they are actually very subjective. I have seen people required to check bags that seemed fine but didn't fit in the little size box thing. I have also seen people board with HUGE backpacking packs. There seem to be many factors when it comes to getting your luggage on the plane: the airline, how full your flight is and how much sleep the airline attendant got the night before.
With that being said, this site takes a fairly legalistic view of a fit; it either fits or it doesn't, with a little wiggle room. Don't be surprised if a bag you own does not (technically) fit on any airlines. This does not mean that it will never fit in overhead storage.
If you hover over each airline fit, you will see an explanation of why we came to that decision. If any dimension (Length or Width or Depth) is over the limit by 1 centimeter, then we deem it as a no-fit (red). If it's within 1 centimer (on any dimension) then we deem it a maybe (yellow). If all are under the airline limit, then we consider it a fit (green).
The combination of all these fits, maybes and no-fits come together to produce the luggage 0-10 score. We also score each region, in case you only fly in a specific area.
Take the numbers here as a guide, not a rule for which luggage to go with. If a bag is close to the limit and you love it, get that one! In most cases, you will be fine when it comes to getting on the plane.
If you have any questions you can email here. Of course, this is a pet project, so I may not have time to respond promptly.