I've read that Mickey Mouse is 2'3", and if you put Donald next to him they're about the same height. Also, in A Day In the Life of Donald Duck (you can watch it on YouTube) you'll see that Donald is really small compared to the humans in the studio and they even have to put another doorknob below the normal one on each door so the toons can go through them. With all this I'd have to say that Scrooge and his relatives are about 2'3". Their furniture & things are probably also smaller than ours to adjust to their height, so they look normal size in the cartoons.