Loading the calculator…
Show your work
Every number on this page comes from one of these.
Take them with you. If our arithmetic and your pencil disagree, we want to hear about it.
Geometry
P = 2 × (L + W)P = 4 × SP = 4 × √(43,560 × A) ≈ 834.8 × √AW = √(43,560 × A ÷ r) · L = r × W · P = 2 × W × (1 + r)P = π × 2 × √(43,560 × A ÷ π) ≈ 739.8 × √AConductor
C_raw = P × strandsC_need = ⌈C_raw × (100 + spare) ÷ 100⌉C_gate = gates × 8 ftC_total = C_need + C_gateHardware
N_line = ⌈P ÷ spacing⌉ − cornersN_ins = N_line × strands · N_strain = corners × strandsPower and grounding
miles = C_raw ÷ 5,280J = max(1, roundUp₀.₅(miles)) · doubled under vegetation loadrods = max(3, table(J), ⌈3J ÷ 6⌉)Paddocks
N = ⌈rest ÷ graze⌉ + 1A_p = A ÷ NC_move = ⌈2 × W × strands × (100 + spare) ÷ 100⌉C_all = ⌈(N − 1) × W × strands × (100 + spare) ÷ 100⌉C_lane = 2 × L × lane strands · L_cross = (W − lane width) ÷ 2The same table the rotational grazing guide prints
Published subdivision guidance next to what this calculator returns. They agree to within a rounding step, which is the point — a tool that disagrees with its own guides is a tool nobody should trust.
| Area | Guide | This calculator |
|---|---|---|
| 1 acre | 835 ft | 834.8 ft |
| 2 acres | 1,180 ft | 1,180.6 ft |
| 3 acres | 1,450 ft | 1,446.0 ft |
| 4 acres | 1,670 ft | 1,669.7 ft |
| 5 acres | 1,870 ft | 1,866.8 ft |
Guides
Read this before you build
Three guides, no fluff, written from the same numbers this page used.
FAQ
The arithmetic questions
- How much electric fence wire do I need for 1 acre?
- A square acre is about 835 ft around. At three strands that's 2,505 ft of conductor, or 2,756 ft once you add 10% for corners, dips and terminations.
- How many paddocks do I need for rotational grazing?
- Rest days divided by grazing days, plus one for the paddock they're standing in. Thirty days of rest with three-day moves gives eleven paddocks; five-day moves give seven.
- How many strands for horses, goats, cattle or deer?
- Horses: three permanent, two seasonal, one interior. Goats and sheep: five, four, two. Cattle: two, two, one. Deer: three, at roughly 18, 34 and 50 inches. The perimeter counts for goats and cattle are manufacturer species guidance rather than extension guidance.
- How much polywire for 5 acres?
- A square five acres is about 1,867 ft around, so each cross-fence spans roughly 467 ft. If you own two reels and move them, that's about 1,030 ft of line out at once — one 1,640 ft roll covers it.
- How many ground rods does an electric fence need?
- Three at minimum: galvanized, 6 ft deep, 10 ft or more apart, for energizers up to 15 joules. Five up to 25 joules, seven up to 35.
- What size energizer do I need?
- Roughly one output joule per mile of total fence, doubled if grass and brush will touch the line. Size it low and the far corner is where you'll find out.
Good fences let you sleep.