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Fence calculator

Fence calculator: posts, rails, pickets and bags of concrete for a straight fence run, from its length, post spacing, picket width and gap.

更新于 已验证的示例：4

Two for fences up to about 4 ft, three for 6 ft privacy fences.
0 for a closed privacy fence.
%
更多选项
A 4 × 4 post is 3½ in square; a 6 × 6 is 5½ in.
About three times the post width.
Quikrete: dig ⅓ to ½ of the post's above-ground height plus 6 in for a gravel base, and stop the concrete 3–4 in below ground. Enter the depth that gets concrete.
试一试
Posts
posts
Posts: 14 posts
整数；向正无穷方向
Sections
13
Rails
26rails
Pickets
252pickets
Concrete for posts
16.11ft³ / 456.2L
Concrete bags
27bags

A 100 ft run with posts every 8 ft needs 14 posts, 26 rails and 252 pickets. Setting the posts takes 16.1 ft³ of concrete, 27 bags of 80 lb.

Fence plan

100 ft8 ft14 posts, 13 sections
计算方法 S

  1. Sections and posts

    ⌈1008⌉=13 sections⇒14 posts\left\lceil \frac{100}{8} \right\rceil = 13\ \text{sections} \Rightarrow 14\ \text{posts}

    Rounded up; a straight run has one more post than sections. The last section is 4 ft.

  2. Rails

    13×2=2613 \times 2 = 26

  3. Pickets

    1,200 in3.5+1.5×1.05=252⇒252\frac{1{,}200\ \text{in}}{3.5 + 1.5} \times 1.05 = 252 \Rightarrow 252

    Each picket takes its own width plus one gap. Rounded up.

  4. Concrete per post

    (π×52−3.52)×30=1,988.69449 in3=1.150865 ft3\left(\pi \times 5^2 - 3.5^2\right) \times 30 = 1{,}988.69449\ \text{in}^3 = 1.150865\ \text{ft}^3

    The hole volume minus the part of the post inside it.

  5. Bags

    ⌈1.150865×140.6⌉=27\left\lceil \frac{1.150865 \times 14}{0.6} \right\rceil = 27

    Rounded up to whole bags; yield per 80 lb bag from Quikrete/Sakrete data sheets.

关于Fence calculator

A straight fence has one more post than it has sections, and sections are the length divided by the post spacing, rounded up. Rails are sections × rails per section. Pickets are the length divided by one picket width plus one gap, with a margin for spares. Concrete per post is the hole's cylinder minus the square post inside it, times the concrete depth.

The default 100 ft run with posts 8 ft apart has 13 sections, 14 posts, 26 rails and 252 pickets 3½ in wide with 1½ in gaps. Setting the posts in 10 in holes with 30 in of concrete takes 16.1 ft³, or 27 bags of 80 lb mix at Quikrete's 0.60 ft³ per bag.

For an L-shaped or enclosed fence, run the calculator once per straight side and subtract one post for each shared corner.

计算示例

100 ft run, 8 ft spacing, 3½ in pickets with 1½ in gaps

Fence length
100 ft
Post spacing
8 ft
Rails per section
2
Picket width
3.5 in
Gap between pickets
1.5 in
Extra pickets
5%
Concrete bag
80 lb (0.60 ft³)
Sections
13
Posts
14 posts
Rails
26 rails
Pickets
252 pickets
Concrete for posts
16.11 ft³
Concrete bags
27 bags

核验来源：Python decimal: ⌈100/8⌉ = 13 sections, 14 posts; 1200 in ÷ 5 in = 240 × 1.05 = 252; (π·5² − 3.5²) × 30 in³ × 14 = 16.11 ft³ ÷ 0.6 = 26.9 → 27

Edge: 80 ft divides into whole 8 ft sections

Fence length
80 ft
Post spacing
8 ft
Rails per section
2
Picket width
3.5 in
Gap between pickets
1.5 in
Extra pickets
5%
Concrete bag
80 lb (0.60 ft³)
Sections
10
Posts
11 posts
Rails
20 rails

核验来源：Hand calculation: 80 ÷ 8 = 10 sections exactly, one more post than sections

Metric 30 m run, 2.4 m spacing, three rails

Fence length
30 m
Post spacing
2.4 m
Rails per section
3
Picket width
90 mm
Gap between pickets
30 mm
Extra pickets
5%
Post width (actual)
90 mm
Post hole diameter
250 mm
Concrete depth in each hole
600 mm
Concrete bag
50 lb (0.375 ft³)
Posts
14 posts
Rails
39 rails
Pickets
263 pickets
Concrete for posts
344.3 L
Concrete bags
33 bags

核验来源：Python decimal: 12.5 → 13 sections; 30000 ÷ 120 = 250 × 1.05 = 262.5 → 263; (π·125² − 90²) × 600 mm³ × 14 = 344.3 L ÷ 0.375 ft³

Closed privacy fence, no gap

Fence length
50 ft
Post spacing
8 ft
Rails per section
3
Picket width
5.5 in
Gap between pickets
0 in
Extra pickets
0%
Post width (actual)
5.5 in
Post hole diameter
12 in
Concrete depth in each hole
36 in
Concrete bag
80 lb (0.60 ft³)
Posts
8 posts
Pickets
110 pickets
Concrete bags
24 bags

核验来源：Python decimal: 600 in ÷ 5.5 = 109.1 → 110; (π·6² − 5.5²) × 36 × 8 posts = 13.81 ft³ ÷ 0.6 → 24

常见问题

How many fence posts do I need?

One more than the number of sections. Divide the fence length by the post spacing and round up to get sections, then add 1: a 100 ft run at 8 ft spacing is 12.5, rounded up to 13 sections and 14 posts, with a last section of 4 ft. For a fence with corners, count each side separately and subtract one post for every shared corner.

How deep should fence posts be set?

Quikrete's guide says to dig one third to one half of the post's above-ground height, plus 6 in for a gravel base, and to make the hole three times the post's width. A post standing 6 ft out of the ground needs a 30–42 in hole, 10½ in wide for a 3½ in 4 × 4. For load-bearing posts, Quikrete refers you to local building codes.

How many bags of concrete do I need per fence post?

Divide the concrete in each hole by the bag's yield. A 10 in hole with 30 in of concrete around a 4 × 4 post holds 1.15 ft³. Quikrete's data sheet gives 0.60 ft³ per 80 lb bag of Concrete Mix, 0.45 ft³ per 60 lb and 0.30 ft³ per 40 lb, so that post takes 2 bags of 80 lb, 3 of 60 lb or 4 of 40 lb.

How many pickets do I need for a fence?

Divide the fence length by one picket's width plus the gap. For 100 ft (1,200 in) of 3½ in pickets with 1½ in gaps that is 1,200 ÷ 5 = 240, or 252 with 5% extra for splits and cuts. A closed privacy fence of 5½ in boards with no gap needs 1,200 ÷ 5.5 = 218.2, so 219 boards before any extra.

How long before a concrete fence post can take weight?

With Quikrete Concrete Mix, which is mixed with water before it goes in the hole, the data sheet says to wait 24 hours before the post is subjected to any strain. Quikrete's fast-setting concrete is poured dry into the hole, then water is added, and it sets in 20 to 40 minutes.

“Fence calculator”有多准确？

准确性取决于输入值和方法的假设。十进制运算使用50位有效数字，但估算、数值方法和源数据的精度可能较低；显示时的舍入并不能消除这些限制。 已按独立来源核验的计算示例：4。 例如，“100 ft run, 8 ft spacing, 3½ in pickets with 1½ in gaps”根据Python decimal: ⌈100/8⌉ = 13 sections, 14 posts; 1200 in ÷ 5 in = 240 × 1.05 = 252; (π·5² − 3.5²) × 30 in³ × 14 = 16.11 ft³ ÷ 0.6 = 26.9 → 27进行核验。

这种方法出自哪里？

Quikrete — setting posts in concrete (hole 3× post width, depth ⅓–½ of the above-ground height plus 6 in of gravel); Quikrete Concrete Mix (No. 1101) data sheet — bag yields 40 lb 0.30, 60 lb 0.45, 80 lb 0.60 ft³.

关于此计算器

posts=⌈Ls⌉+1,pickets=⌈Lwp+g(1+extra)⌉,Vpost=(πD24−a2)h\text{posts} = \left\lceil \frac{L}{s} \right\rceil + 1,\quad \text{pickets} = \left\lceil \frac{L}{w_p + g}(1 + \text{extra}) \right\rceil,\quad V_{\text{post}} = \left(\pi \tfrac{D^2}{4} - a^2\right) h

来源

  1. Quikrete — setting posts in concrete (hole 3× post width, depth ⅓–½ of the above-ground height plus 6 in of gravel)
  2. Quikrete Concrete Mix (No. 1101) data sheet — bag yields 40 lb 0.30, 60 lb 0.45, 80 lb 0.60 ft³

已对照来源验证

此计算器包含 4 个已解示例，答案来自独立来源。这些示例会在测试套件中运行，你也可以在此运行验证。

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