Upvote:4
It depends on the airline, and the geographic area.
For example, transatlantic Delta flights are quite cold (typically around 20C/70F, could be 18C). I've been on like 50 of them, and they all were like that.
However all transatlantic flights I've been on on Lufthansa (only 6 or 8 though) were all uncomfortably warm (25C), and the staff said "we always keep it like that".
Now, Delta flights between Tokyo and Shanghai, or Tokyo and Manila are warm. Probably around the same 25C as Lufthansa ones.