Fence Calculator
Calculate fence posts, rails, and pickets. Enter values for instant results with step-by-step formulas.
Formula
Posts = (Length / Spacing) + 1
Divide fence length by post spacing, add 1 for the final post. Calculate rails and pickets based on fence sections and desired spacing.
Worked Examples
Example 1: Backyard Privacy Fence
Problem:100 ft long, 6 ft tall, 8 ft post spacing, 3 horizontal rails, pressure-treated wood.
Solution:Posts needed:\n(100 / 8) + 1 = 13.5 → 14 posts\nPost length: 6 + 2 = 8 ft (4×4)\n\nRails (8-ft 2×4s):\n(100 / 8) sections × 3 rails = 39 rails\n\nPickets (6-ft 1×4s, 4\" spacing):\n(100 ft × 12 inches) / 4 = 300 pickets\n\nConcrete (1.5 bags per post):\n14 × 1.5 = 21 bags (50-lb)\n\nCost:\n14 posts × $15 = $210\n39 rails × $8 = $312\n300 pickets × $2 = $600\n21 bags × $7 = $147\nTotal: ~$1,269 materials
Result:14 posts | 39 rails | 300 pickets | $1,269
Example 2: Small Garden Fence
Problem:50 ft, 4 ft tall, 6 ft post spacing, 2 rails.
Solution:Posts:\n(50 / 6) + 1 = 9.3 → 10 posts (6-ft)\n\nRails:\n(50 / 8) sections × 2 = 13 rails (2×4 × 8 ft)\n\nPickets:\n(50 × 12) / 4 = 150 pickets (4-ft)\n\nConcrete:\n10 × 1.5 = 15 bags\n\nCost:\n10 posts × $12 = $120\n13 rails × $7 = $91\n150 pickets × $1.50 = $225\n15 bags × $7 = $105\nTotal: ~$541
Result:10 posts | 13 rails | 150 pickets | $541
Example 3: Property Line Fence with Gates
Problem:200 ft, 6 ft tall, 8 ft spacing, with 2 single gates (4-ft wide each).
Solution:Posts:\n(200 / 8) + 1 = 26 line posts\nAdd 4 for gates (2 per gate)\nTotal: 30 posts (8-ft, 4×4)\n\nRails:\n(200 / 8) × 3 rails = 75 rails (2×4 × 8 ft)\n\nPickets:\n(200 × 12) / 4 = 600 pickets (6-ft)\n\nConcrete:\n30 posts × 1.5 = 45 bags\n\nGates:\n2 gates × $250 = $500 (materials)\n\nTotal materials: ~$2,950 + gates
Result:30 posts | 75 rails | 600 pickets + 2 gates
Frequently Asked Questions
How many fence posts do I need?
Formula: (Fence length / Post spacing) + 1. Standard spacing is 8 feet on-center for residential privacy fences. For 100-ft fence: (100 / 8) + 1 = 13.5 → 14 posts total. Add 2 posts per gate opening (gates need posts on both sides regardless of spacing alignment). Add extra for corners (each corner needs a post). Closer spacing (6 ft): Stronger fence, more posts, more cost - good for tall or heavy fences, high-wind areas. Wider spacing (10 ft): Economy choice but requires stronger posts/rails. Always buy 1-2 extra posts for mistakes, damage, or future repairs. Posts are critical structural component - don't skimp on quantity or quality.
How deep should fence posts be buried?
General rule: Bury 1/3 of total post length underground. 6-ft fence: Use 8-ft posts with 2 ft underground. 4-ft fence: Use 6-ft posts with 2 ft underground. 8-ft fence: Use 10-ft posts with 2.5-3 ft underground. Frost line considerations: In cold climates, posts must extend below frost line (18-48\" depending on region) to prevent frost heaving. Sandy/loose soil: Dig deeper (30-36\") or use larger concrete footings. Corner and gate posts: Often need 6-12\" deeper for added lateral strength. Post hole diameter: 3× post width (12\" hole for 4×4 post). Check local code for frost line requirements - non-compliance = inspection failure and frost damage.
What size fence posts should I use?
4×4 posts (3.5\" × 3.5\" actual): Standard for residential fences up to 6 ft tall, line posts (between corners). 6×6 posts (5.5\" × 5.5\" actual): Corner posts, gate posts, fences taller than 6 ft, high-wind areas, extra strength. Post length = Fence height + buried depth: 6-ft fence = 8-ft posts (6 ft above + 2 ft below). 4-ft fence = 6-ft posts (4 ft above + 2 ft below). Material: Pressure-treated wood (rated for ground contact - .40 retention minimum), cedar (naturally rot-resistant but expensive), steel (T-posts or pipe, very durable). Never use untreated wood underground - will rot within 3-5 years. Always use pressure-treated rated for ground contact, not just above-ground.
How much concrete per fence post?
Standard 4×4 post in 8-inch diameter hole, 24\" deep: ~1.5 bags (50-lb) fast-setting concrete or 0.5 cubic feet wet mix. Calculate: Volume = π × r² × depth = 3.14 × (4\")² × 24\" = 1,206 cu in ÷ 1,728 = 0.7 cu ft. One 50-lb bag makes ~0.375 cu ft, so need 2 bags per post. Larger 6×6 posts or deeper holes: 2-3 bags per post. For 14-post fence: 28 bags (1.5 each) or 42 bags (3 each for strong fence). Fast-setting concrete ($7-10 per bag): Mix dry in hole, add water, sets in 20-40 minutes. Regular concrete ($5-7 per bag): Requires mixing, 24-48 hour cure. Alternative: Gravel backfill (better drainage, less strength) for light fences only.