I'm surprised people wouldn't have a rough idea of what feet is. For all the crap Americans get for supposedly not knowing other units, I think most of us have a pretty good idea of what a meter is. It's close enough to say it's about 3 feet.
I'd guess that more people from Europe would understand "33,000 feet", than Americans would understand "10,000 metres"
Ah, more anti-American prejudices...
As an American living in Europe, I can say with a million percent certainty that Europeans know vastly less about US customary units than Americans know about metric. (As in, the average European knows literally
nothing about customary units. Which makes sense, since they aren’t taught them in school.)
Americans are taught metric in school (even if customary units are used more), so we grow up with an inkling of what metric units are. We at least know that a meter is very broadly speaking about the same general length as a yard (3 feet). We have a pretty good feel for what mm and cm are: American rulers invariably have inches on one side and cm/mm on the other. (Oddly, measuring tapes do not.) Analog thermometers have both scales, as did traditional analog speedometers in cars. Americans are passively exposed to metric on a daily basis in all areas of life. Europeans (and presumably other non-North and South Americans) simply aren’t
ever exposed to US customary units except in very specific circumstances that most people do not encounter on a regular basis.
So no, people from Europe wouldn’t know what to make of 33,000 feet. An American might be able to say “hmmm, that’s about 6 miles”, a European will have no clue that it’s 10km.