1 acre = 43,560 square feet. It can be any shape, as long as the enclosed area is 43,560 square feet. If it's square, then each side of the square is 208.71 feet long. If it's a circle
http://wiki.answers.com/Q/How_big_is_1_acres

One acre equals 43,560 square feet, or 4,840 square yards. So 280 ft would be equal to .0064279
http://www.chacha.com/question/howbigis1acre

One acre is 43,560 square feet. It can be comprised in any shape and size as long as the total equals 43,560 square feet. Here is a lot 165 feet by 264 feet. and another lot at 198
http://answers.yahoo.com/question/index?qid=200802...
