The Big Issue: Carry-on baggage limits

How flexible are airlines' carry-on allowances? It's a question many of us deal with and there are good reasons why we might be inclined to bend the rules.

Flying with just a carry-on bag means saving the check-in baggage fee if we're aboard a low-cost carrier or on a super cheap ticket, and there is no dallying around the baggage carousel at the far end.

Then again, if you're travelling with fragile and valuable electronics – a laptop, a tablet, expensive camera or video gear – you probably aren't inclined to pack them in your checked baggage.

There's a common thread running through most airlines carry-on limits. If you're flying economy or premium economy the general limit is one bag with a maximum weight of seven kilograms plus one small personal item, such as a handbag or a laptop bag. Aboard a low cost carrier that total is likely to include whatever small personal item you might be toting as well as your cabin bag.

However, Air China and China Southern, based in the People's Republic of China, apply a frugal five-kilogram carry-on limit to their economy flyers. At the other end of the scale, American Airlines and United do not specify a weight limit for carry-ons on their websites.

Some airlines are more rigorous in enforcing their carry-on limits and the low-cost carriers are the most likely to play hardball. Jetstar is known for its random spot checks. At the gate, passengers' carry-ons might be weighed. Any economy flyer boarding an international Jetstar flight with more than the allocated seven kilograms risks a $160 on-the-spot penalty.