Your Result Explained: What These Numbers Mean
Building a straight, wind-resistant wood fence requires converting total linear footage into structural bays, posts, horizontal stringer rails, vertical pickets, and cylindrical post-hole concrete footings. Because nominal lumber sizes differ from actual dressed dimensions—a nominal "1×6" fence picket actually measures 5.5 inches wide, and a "1×4" picket measures 3.5 inches wide—calculating pickets using nominal numbers leaves you 9% short before you even open your first bundle of lumber.
Bays & Posts shows the number of 6-foot or 8-foot fence sections (bays) plus the terminal end post and any extra gate-framing posts. Total Rails adjusts the horizontal 2×4 stringers (2 per bay for 4 ft fences, 3 per bay for 5–6 ft fences, 4 per bay for 8 ft fences) by your lumber waste percentage. Pickets & Fasteners gives the waste-adjusted count of vertical boards and exterior ring-shank nails or deck screws (2 fasteners per picket-to-rail intersection). Finally, the Concrete Footings section subtracts the underground volume of the 3.5" × 3.5" wood post from each cylindrical auger hole to give you the exact number of 80 lb or 60 lb concrete bags required.
Worked Example: 100 Ft Privacy Fence (6 Ft Tall, 1 Gate)
A homeowner is building 100 linear feet of 6-foot tall zero-gap privacy fence with 8-foot post spacing, 1×6 dog-ear pickets (5.5" actual width), 1 walk gate, 10-inch diameter by 30-inch deep post holes, and a 10% waste factor.
- Calculate 8 ft fence bays: ⌈100 ft ÷ 8 ft⌉ = 13 bays.
- Compute 4×4 posts: 13 bays + 1 end post + 1 gate post = 15 posts.
- Calculate 2×4 horizontal rails (3 rails per bay for 6 ft height): 13 × 3 = 39 net rails × 1.10 = 43 rails.
- Compute 1×6 pickets (5.5" width, 0" gap): (100 ft × 12 in/ft) ÷ 5.5 in = 218.18 net × 1.10 = 240 pickets.
- Calculate fasteners (2 screws per rail × 3 rails): 240 pickets × 6 screws = 1,440 screws.
- Compute net concrete per 10" × 30" hole: [π × (5/12)² × 2.5 ft] − [(3.5/12)² × 2.5 ft] = 1.3635 − 0.2127 = 1.1509 cu ft/post.
- Convert 15 posts (+10% waste) to 80 lb bags: (15 × 1.1509 × 1.10) ÷ 0.60 cu ft/bag = 32 bags of 80 lb concrete.
Result Summary: Order 15 posts (4×4×8'), 43 horizontal rails (2×4×8'), 240 dog-ear pickets (1×6×6'), 1,440 exterior screws, and 32 bags of 80 lb concrete.
How This Is Calculated (Formulas & Measurement Guide)
Our fence calculator divides linear fence length by on-center post spacing to determine structural bays and posts, uses NIST PS 20 actual dressed picket widths plus gap spacing to count pickets, and calculates true cylindrical concrete volume per hole after subtracting the displaced volume of the buried 4×4 post.
Bays = ⌈Length ÷ Post Spacing⌉ | Posts = Bays + 1 + Gates | Rails = ⌈Bays × Rails/Bay × (1 + Waste%)⌉ Every continuous fence line requires 1 more post than the number of bays, plus 1 additional king/latch post per gate opening.
Pickets = ⌈[(Length Ft × 12) ÷ (Actual Picket Width In + Gap In)] × (1 + Waste%)⌉ Divides total fence length in inches by the repeating module of one picket plus one gap (5.5" for tight 1×6 privacy, or 3.5" + gap for spaced picket fences).
Hole Concrete (ft³) = [π × (Dia/24)² − (3.5/12)²] × (Depth/12) × Posts × (1 + Waste%) Subtracts the 3.5" × 3.5" cross-section of a dressed 4×4 wood post from the cylindrical auger hole, then divides by 0.60 ft³ (80 lb bag) or 0.45 ft³ (60 lb bag).
How to Measure Irregular Areas & Curved Borders
Run a stake-and-masons-string line along your planned fence perimeter and measure each straight run separately in feet. Always call 811 at least 3 business days before augering post holes so underground gas, electric, and fiber lines are marked.
Practical Tips & Common Mistakes to Avoid
Field-Tested Planning Tips
Bury 1/3 of the Total Fence Post Length + 4 Inches of Gravel
For a 6-foot tall fence, use 8-foot or 9-foot 4×4 posts buried 24 to 36 inches deep (and always below your local winter frost line). Pour 4 inches of #57 crushed stone into the bottom of each hole before setting the post so water drains away from the end grain.
Crown the Top of Concrete Footings Above Soil Grade
Fence posts rot most frequently right at the soil collar where moisture and oxygen meet. Slope the top of your wet concrete footing 1 inch above grade and trowel a smooth bevel away from the 4×4 wood post so rainwater sheds outward.
Use a Spacer Jigs and Top String Line for Pickets
Never follow undulating ground with the top of your pickets unless you are intentionally contouring a slope. Stretch a tight mason line 6 inches above the top rail from corner post to corner post to keep picket tops dead level.
Choose Hot-Dipped Galvanized or Stainless Ring-Shank Fasteners
Modern ACQ and copper-azole pressure-treated lumber and acidic Western Red Cedar corrode standard electro-galvanized nails rapidly, leaving black streaks down your pickets. Use only ASTM A153 hot-dipped galvanized or 305/316 stainless steel screws or ring-shank nails.
Common Ordering & Installation Mistakes
Mistake Using 6-inch nominal width instead of 5.5-inch actual width for pickets
Recommended Fix: Calculating 100 feet (1,200 inches) ÷ 6 inches gives 200 pickets, whereas actual 5.5-inch 1×6 boards require 219 net pickets (240 with 10% waste). Our calculator uses exact 5.5" and 3.5" NIST dressed widths.
Mistake Butting green pressure-treated privacy pickets tightly with zero expansion gap
Recommended Fix: Wet pressure-treated pickets shrink by 1/8 to 1/4 inch as they dry in the sun, while kiln-dried cedar swells when rained on. Use a thin 8d nail as a 1/8-inch spacer when installing kiln-dried cedar so wet boards do not buckle.
Mistake Building a 6-foot privacy fence with only 2 horizontal rails per bay
Recommended Fix: With only a top and bottom rail on a 6-foot fence, the middle of the pickets warps and bows in the sun. Always install 3 horizontal 2×4 rails per bay on 5-foot and 6-foot fences.
Mistake Hanging a heavy walk gate on an unbraced 4×4 post with 1 bag of concrete
Recommended Fix: Gate hinge posts carry constant cantilever torque. Use a 4×6 or 6×6 post (or heavy-wall steel post) for gate hinge sides and dig the gate footing 36 inches deep.
6-Foot Privacy Fence Material Reference Table (8 Ft Post Spacing)
Material quantities for a 6-foot tall zero-gap privacy fence using 5.5" actual (1×6) pickets, 3 rails per bay, and 10" × 30" post holes (includes +10% lumber/concrete waste).
| Fence Length | 8 Ft Bays | 4×4 Posts (No Gates) | 2×4 Rails (3/Bay, +10%) | 1×6 Pickets (Zero Gap, +10%) | 80 lb Concrete Bags (+10%) |
|---|---|---|---|---|---|
| 50 ft | 7 | 8 | 24 rails (21 net) | 120 pickets (110 net) | 17 bags |
| 100 ft | 13 | 14 | 43 rails (39 net) | 240 pickets (219 net) | 30 bags |
| 150 ft | 19 | 20 | 63 rails (57 net) | 360 pickets (328 net) | 43 bags |
| 200 ft | 25 | 26 | 83 rails (75 net) | 480 pickets (437 net) | 55 bags |
| 300 ft | 38 | 39 | 126 rails (114 net) | 720 pickets (655 net) | 83 bags |
Reference Source: Source: NIST PS 20 American Softwood Lumber Standard (1×6 actual width = 5.5", 4×4 post = 3.5"×3.5") & Quikrete 80 lb bag yield (0.60 cu ft). Standard ready-mix concrete weighs ~4,000 lbs (2 tons) per cubic yard cured.
Frequently Asked Questions (Fence Calculator)
How many 1×6 fence pickets do I need for 100 feet of privacy fence?
Because a nominal 1×6 picket actually measures 5.5 inches wide, 100 linear feet (1,200 inches) with zero gap requires 219 net pickets. Adding a standard 10% allowance for warped or split boards means you should order 240 pickets.
How many bags of concrete do I need per fence post?
A standard 10-inch diameter hole dug 30 inches deep around a 4×4 post holds 1.15 cubic feet of concrete—which equals roughly two 80 lb bags (0.60 cu ft each) or two-and-a-half 60 lb bags (0.45 cu ft each) per post.
Should I space fence posts 6 feet or 8 feet apart?
Eight-foot on-center spacing is the residential standard for most 4-foot to 6-foot wood fences. However, if you live in a high-wind coastal or plains region, or are building an 8-foot tall privacy fence, reducing post spacing to 6 feet increases wind load resistance by over 30%.
How deep should fence post holes be dug?
Dig fence post holes to a depth equal to 1/3 to 1/2 of the above-ground fence height (24 to 30 inches for a 6-foot fence), or 6 inches below your local winter frost line—whichever is deeper.
How many horizontal 2×4 rails do I need per fence section?
Use 2 rails per bay for 4-foot picket fences, 3 rails per bay for 5-foot and 6-foot privacy fences, and 4 rails per bay for 8-foot tall privacy or security fences.
Can I pour dry concrete mix into the post hole and add water on top?
While fast-setting dry-pour mixes are acceptable for light 4-foot fences in damp soil, machine-mixing or tub-mixing standard 80 lb concrete with water before pouring around the post eliminates dry air pockets and produces a much stronger footing for 6-foot privacy fences and gate posts.
Worked Example Project Scenarios (Fence Calculator)
Explore pre-computed material takeoffs for popular residential project dimensions: