How much fence twenty acres take
Twenty acres are 871,200 square feet. Fenced as a square, each side is 933.4 ft and the fence around it is 3,734 ft, 0.71 miles. As a 2:1 rectangle the sides come out at 1,320 by 660 ft, a quarter mile by an eighth, with 3,960 ft of fence: 226 ft or 6% more.
Fence = 4 × √(acres × 43,560) for a square, 6 × √(acres × 43,560 ÷ 2) for a 2:1 rectangle
Worked example: why the longer fence needs fewer wood posts
At twenty acres the side lengths cross the University of Kentucky's 660 ft bracing limit, and that turns the usual rule about shape on its head. Kentucky braces a run up to 660 ft with a double H-brace at each end and adds a braced pull post every 660 ft beyond. With 4 strand barbed wire, T-posts every 12 ft and one 12 ft gate:
| Square, 933 × 933 ft | Rectangle, 1,320 × 660 ft | |
|---|---|---|
| Fence after the gate | 3,722 ft | 3,948 ft |
| T-posts | 335 | 357 |
| Pull posts | 3 | 1 |
| Brace posts | 26 | 22 |
| Wood posts in total | 35 | 29 |
| Barbed wire, 1,320 ft rolls | 13 | 14 |
| Installed | $4,800 to $22,930 | $5,090 to $24,290 |
Each 933 ft side of the square is too long for a double brace alone, so three of them get a pull post; the fourth is split by the gate into two 460.7 ft runs that don't. The rectangle's 660 ft short sides sit exactly on the limit, and only the long side without the gate needs a pull post. So the rectangle takes 22 more T-posts and a roll more wire, but 6 fewer wood posts to set and brace. The University of Georgia sets end posts at least 4 ft deep against 2 ft for line posts, so each wood post you avoid is a deep hole saved. When you can choose the layout, sides in multiples of 660 ft brace efficiently.
How far apart should pull posts be?
Extension guides disagree, and the difference matters at this size:
- University of Kentucky: braced pull posts on runs over 660 ft, and bracing every 660 ft on suspension fence.
- University of Georgia: braced line assemblies "every 650 ft", plus at the foot and top of hills.
- NRCS California: in line H-brace pull assemblies every 1,320 ft, the "length of a spool of wire".
The calculator uses Kentucky's 660 ft. Under the NRCS California spacing, neither shape here needs any pull posts, which saves 3 wood posts and 6 brace posts on the square. On rolling ground, add Georgia's assemblies at the top and bottom of each hill to whichever rule you follow.
Splitting twenty acres into paddocks
To graze in rotation, cutting the square into four five acre paddocks takes two cross fences, each 933 ft, so 1,867 ft of interior fence on top of the 3,734 ft perimeter. Each paddock is then a 466.7 ft square. Enter the interior lines as a separate total length in the calculator below to count their posts.
What twenty acres cost by fence type
Iowa State University Extension's 2024 budget, priced for Iowa with labor at $20 an hour, gives per foot figures that we can apply to the square's 3,722 ft: about $5,250 for woven wire at $1.41, $4,320 for 5 strand barbed at $1.16, and $3,420 for non-electric high tensile at $0.92. All three sit below the low end of the national installed ranges in the table, which come from HomeAdvisor and Fixr. High tensile has the narrowest range, $4,620 to $9,900, and needs 159 T-posts and 6 rolls of 4,000 ft wire. HomeAdvisor gives $150 to $600 for each livestock gate you add.
For a mile of fence, see the 40 acre page; for cattle on half this area, the 10 acre page. The farm fence calculator covers livestock fence in general, and the fence calculator covers every style.