Are carry-on bags being weighed on long-haul flights?

Whether your cabin baggage gets weighed really depends on what airport and what airline you are flying with. With most full-service airlines, they don't bother weighing baggage as long as it meets the size restrictions - and sometimes they don't even check that. The bit about size restrictions is because at some airports, at a security counter itself they flag oversized items and ask you to go back and check it in instead. Usually, there are metal enclosures which they place the baggage into - if it fits, it's good to go.

With low-cost airlines, it's a bit different. In Europe, I have seen they mostly just care about the size rather than weight. In Asia though, low-cost airlines sometimes do also weigh to see if its within the weight limits. The reason why I said it depends on the airport as well as the airline is because, just to take an example, if you're flying out of Singapore's Changi Budget Terminal used by low-cost airlines then there's a centralised size and weight check carried out by airport security, and anything (visibly) overweight is weighed and excess baggage fees collected. Flying with the same airline at a different airport (on the return flight) the other airport may not do the same check.

Don't worry about this too much. The size and weight restrictions, as most airlines mean it, is more as guide for what can safely be stowed in overhead bins or under seats. Most airlines understand that sizing is not standard, so weight is a 'safer' way of defining a guideline of what you should be aiming to carry on board as luggage. As long as it's not visibly bulky, airlines and airport security won't stop you or charge you extra fees for carrying anything onboard.

Emirates weighed my carry-on bag on a long-haul flight from NYC to Dubai in April 2011, and made me check it since it weighed 25 lbs (12 kg) which was over the limit of 15 lbs (7kg). It was definitely carry-on size by dimensions. I was very surprised (and annoyed since I wouldn't have tried to take the carry-on sized bag if I knew I had to check it.) It's not even a matter of packing light since almost any hard frame rolling bag with a handle is going to weigh around 60% of the limit before you even put anything in it.

Given that, I had all my rather dense electronics in a small daypack that was also over the limit by a few pounds, and that was on my back and they didn't give it a second look. So it seems like the weight limit applies to carry-on luggage, but not necessarily carry-on bags.

While returning to the US, KLM at Heathrow recently required that my carry-on bag and personal items be weighed. They then required me to check the carry on for around $100 US - even though it met the size requirement. This was very aggravating, since never before have I been asked to weigh carry on items, and I was not charged when I flew with the same bag on KLM during the originating flight.

A recent experience of mine: Manchester to Orlando, FL with Thomas Cook (large aircraft) with a carry-on luggage within the size limits they asked me to put it on the scales and since it was 12kgs (limit was 6kgs) I was forced to check it in (luckily my ticket included a 23kg allowance).

The very same carry-on flying from Orlando, FL to Memphis, TN with Delta (smaller aircraft) no one ever bothered to check and I took it onboard.

Important detail: Thomas Cook does not provide online check in, thus you can't escape from airport check in, whereas with Delta I had checked in online and went straight through security and then to the gate.

We just returned from New Zealand and took an Air New Zealand flight from Auckland to Christchurch and later Christchurch to Auckland, and while boarding each flight our carry on bags were never weighed. We had a 3 hour layover that dragged into a 6 hour layover due to weather so I watched other Air New Zealand flights board too and no bags were weighed although the over head paging system kept saying the 7kg limit was strictly enforced. I did see many scales near the barding area in Auckland, but nine were used to enforce the 7 kg rule.

Yeah I don't think the US airlines care about carry on weight, but I remember flying from AKL to Fiji I had a little trouble. I had to check in my bag, and the lady made me weigh my carry on. It was 9 kg, and she was giving me a hard time. However she let me go overweight with my check in bag, but it wasn't enough. However right before I boarded the plane, nobody checked my carry on weight. So I guess the the check in lady gave me a hard time for nothing. Which I found kind of annoying. So for Air NZ, it doesn't seem like they strictly enforce their carry on weight based on my experience.

Fiji Airways gave me a harder time unfortunately. My carry on was 9 kg (their limit was 7 kg), and they were almost gonna make me check it in. They also thought my backpack was too large; it's the first airlines to call me out on my backpack. Luckily the manager let it slide by. These carry on rules can be so vague, which makes it frustrating.