Unfortunately there isn't a simple answer to your question. The answer depends on the shape of your land.
If your 51 acres is a square, which it probably isn't, then then the distance around this square is 1.13 miles.
If your 51 acres is a circle, which it probably isn't, then then the distance around this circle is 1.00 miles.
If your 51 acres is a rectangle, oneeighth of a mile wide, which it probably isn't, then then the distance around this rectangle is 1.53 miles.
And, just to see how extreme this can get, if your 51 acres is a very long rectangle 50 yards wide, which it undoubtedly isn't, then the distance around the rectangle is 5.67 miles.
Penny
