Fence Calculator
Calculate how many fence posts, rails, and boards you need for any fencing project based on perimeter and fence design.
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How to Use This Calculator
- Enter the total fence perimeter in feet.
- Enter the post spacing and fence height.
- Enter board width and gap in inches and the number of rails per bay.
Formula
Posts = floor(Perimeter ÷ Spacing) + 1
Boards per bay = ceil(Spacing × 12 ÷ (board width + gap))
Total boards = Boards/bay × (Posts − 1) × (1 + waste%)
Example
Example: 120 ft perimeter, 8 ft spacing, 6 in boards, 0.25 in gap → 16 posts, 3 rails: 48 rails, ~216 boards.
Frequently Asked Questions
- Divide the total fence length by post spacing and add 1 for the starting post. Formula: Posts = (Length ÷ Spacing) + 1. For a 100 ft fence with 8 ft post spacing: 100 ÷ 8 + 1 = 13.5, round up to 14 posts. For a corner fence with two 50 ft runs: each run gets its own calculation — 50 ÷ 8 + 1 = 7.25, round to 8 per run, but the corner post is shared, so total = 8 + 7 = 15 posts. Add gate posts separately; each gate requires two posts set 4 inches wider than the gate opening.
- Standard post spacing for wood privacy fences is 6–8 feet on center. Eight-foot spacing is most common because fence boards and rails are sold in 8-foot lengths, minimizing waste. Six-foot spacing increases rigidity and is recommended on windy sites or for heavier decorative fencing. Chain-link fences typically use 10-foot spacing with lighter gauge posts. Rail fences use 8–10 foot spacing. For any fence over 6 feet tall or in a high-wind region, stick to 6-foot spacing and set posts at least 1/3 of their total length below grade in concrete footings.
- For a standard 8-foot wide privacy fence panel using 6-inch wide boards with a 1/4-inch gap between boards, you need about 15 boards per panel: 8 ft = 96 inches ÷ (6 + 0.25) = 15.3, round to 15 boards. If you use 4-inch boards with 1/4-inch gaps: 96 ÷ 4.25 = 22.6, so 23 boards per panel. This calculator lets you enter your board width and gap to compute the exact count. For a board-on-board pattern (boards overlapping), divide the panel width by the exposed face width of each board instead.
- Horizontal rails run between posts and support the fence boards. A 6-foot tall privacy fence typically needs 3 rails per bay (top, middle, bottom). A fence 4 feet or shorter needs 2 rails. The number of rail spans equals the number of post bays, which is always one less than the number of posts. For example, 14 posts = 13 bays × 3 rails = 39 rail sections. Rails are usually sold in 8-foot or 16-foot lengths. If post spacing is 8 feet, each bay uses one 8-foot rail per level. If post spacing is 6 feet, use 16-foot rails spanning two bays for economy.
- Yes — always add 5–10% extra fence boards to account for end cuts, splits, knots, and boards damaged during installation. For a straight fence with no corners, 5% waste is sufficient. For a fence with multiple corners and sections of different heights, use 10%. For very long fence runs (200+ feet), buy in bulk and use the offcuts from one section as starters for the next, which reduces waste. This calculator includes a configurable waste percentage. Storing a few extra boards from the same purchase batch is also smart because wood from different batches may vary in color and grain.