Why are doors rectangular?

Answer 1

If the door is circle, you will have to bent down in order to come out of the room[or even the house].Same as if the door is square.

this is what the person before me said. i am improving answer. only because i say..... why not make the square huge?

well, as you know, humans are of different sizes, so we can't have a door perfect for your body cos that would be cramped and imagine inviting ppl over! so, instead, architects look for something resembling our body shape. we have(more or less):

1 pair of parelell sides that are the same length

1 pair of parelell sides that are the same length..... what shape is the same?

RECTANGLE! though my granny has a oval door. i have to step up into the house. anyway, my friend has a square door though it uses up space. why pay for more wood? it looks....weird. different, i guess.