How long of an airline flight is too long for you?

The longest I've flown is from London to Las Vegas non stop around 12 hours. Aiming to fly across to Australia next year which will mean 20 hours on a plane....yikes. But I think the length you can comfortably fly for really depends on the person.

I have made the trip from Houston to Singapore several times, it usually takes more than 24 hours!

I actually enjoy flying and never considered any length of journey to be too long. I suppose that there has to be a limit because you cannot fly for days without it becoming restrictive to some degree, but I would say that all current flights are within a reasonable level. My longest flight was a domestic flight in Russia some years ago. I flew from Moscow to Bratsk in Central Siberia (3500 miles) and then to Irkutsk and back to Moscow a couple of days later.

8 hours is just about my upper limit. I'm sure I could go longer if I had to or it was a place I really wanted to visit, but it would definitely be painful. The longest flight I have taken up until now was from the East Coast of the US to Paris, France. That was 8 1/2 hours.

i am looking forward to experience such long flight but I only got 4 hours the most. Hopefully next year my travel from Singapore to Houston will materialized.