How many feet of fencing do I need to fence 1/2 an acre of land?

Ive got a lot that is 21,000 sq ft. So 1/2 an acre and I want to fence it all. How many feet of fencing do I need to buy?|||That's right, it could be 600 linear feet, or 720 linear feet........which would make a big difference. You've got to take measurements! Also what type fence, what height, who's going to install it?, what about posts.....footings?? Gates??|||That depends on the dimensions of your lot. Is it nearly square or a long skinny rectangle?? It makes a difference.