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CalcTheBuild

Fence Calculator

Putting up a privacy fence, a picket fence or a run of prefab panels? Enter the total length, height, corners and gates, and see how many posts, rails and pickets (or panels) to buy, how much concrete the post holes take and what the materials will cost. It works in feet or meters, with US lumber sizes, UK feather edge and panels, and Australian palings.

ft

Add up every side you are fencing, including gate openings.

ft

Each change of direction gets its own post.

ft

Gate openings get no pickets or panels.

ft

Built-on-site fences: 6–8 ft (1.8–2.4 m). Ignored for panels unless you pick “Other” below.

in

0 for a privacy fence; 2–3″ (50–75 mm) for a classic picket fence.

ft

About ⅓ of the height above ground, at least 2 ft (600 mm); go below the frost line in cold climates.

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For example an 8 ft 2 × 4 or a 2.4 m arris rail.

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Your estimate

Fence posts
16 posts
Pickets / boards to buy
231 pickets
Estimated material cost
$1,829.00
Post length (height + depth)
8 ft
Bays between posts
14 bays
Actual post spacing
8 ft
Rails
42 rails
Rails per bay
3 rails
Nails or screws (2 per rail)
1,260 fasteners
Bags of post concrete
40 bags
Bags per post
2.5 bags
Concrete volume
14.73 cu ft
Fence length without gates
96 ft
Posts cost
$288.00
Post concrete cost
$320.00
Rails cost
$252.00
Pickets cost
$693.00
Fasteners cost
$126.00
Gates cost
$150.00
Cost per unit length
18.29 $/ft

Post count: fence length without gates ÷ spacing, rounded up, plus one end post, one extra post per corner and one per gate. Runs rarely divide evenly, so expect to cut the last bay of a run short.

Rails: 2 per bay up to 4 ft (1.2 m) high, 3 up to 6 ft (1.8 m) and 4 above that. Buy pickets at least as long as the fence is high.

Concrete fills the hole to full depth around the post. A 4–6″ (100–150 mm) layer of gravel at the bottom of the hole helps drainage and slightly reduces the concrete.

Check local rules before you build: many areas limit fence height (often 6 ft or 2 m at the back and 3–4 ft or 1 m at the front) and some need a permit. Call 811 (US) or check utility maps before digging.

How to use this calculator

  1. Choose whether you are building the fence on site from pickets and rails, or hanging prefab panels between posts.
  2. Enter the total length of every side you are fencing, the fence height, the number of corners and the number and width of gates.
  3. For a fence built on site, set the post spacing (8 ft or 2.4 m is typical), the picket size and the gap between pickets: 0 for a privacy fence, 2–3″ (50–75 mm) for a picket fence. For panels, pick the panel width instead.
  4. Choose the post size and how deep the posts go into the ground. About a third of the above-ground height, and never less than 2 ft (600 mm), is the usual rule.
  5. Pick your post concrete, keep 10% waste on pickets, and enter local prices for posts, rails, pickets or panels, concrete, gates and fasteners to see the total.

How the fence calculation works

First the gate openings come off the total length. The rest is divided by the post spacing and rounded up to give the number of bays. Each corner adds a bay, because the spacing starts again on every side, and the posts are the bays plus one end post plus one extra post for each gate. For 100 ft of fence with two corners and one 4 ft gate, at 8 ft spacing: 96 ÷ 8 = 12 bays, plus 2 for the corners makes 14 bays, and 14 + 1 + 1 = 16 posts.

A 6 ft fence gets three rails per bay, so 14 × 3 = 42 rails. Butted 1 × 6 pickets (5½″ wide) cover 1,152″ ÷ 5.5 = 209.5, so 210 pickets, or 231 with 10% waste. Two nails or screws per picket at every rail makes 1,260 fasteners.

Each 4 × 4 post sits 2 ft deep in a 10″ hole, so it needs 8 ft posts. The concrete around one post is the hole volume minus the post: about 0.92 cu ft, or 2.5 bags of 50 lb fast-setting mix. Sixteen posts take 14.7 cu ft, which is 40 bags. At $18 per post, $6 per rail, $3 per picket, $8 per bag, $10 per 100 fasteners and $150 for the gate, the materials come to $1,829, about $18.29 per foot of fence.

In metric, 30 m of 1.8 m feather edge fencing with two corners and a 1 m gate needs 17 posts of 2.4 m at 2.4 m spacing, 45 rails, 319 boards of 125 mm and 57 bags of 20 kg post mix.

Pro tips

  • Mark the line with string and set the corner, end and gate posts first. Then space the line posts between them so every bay comes out the same width, rather than ending with one short bay.
  • Crown the top of the concrete so rainwater runs away from the post, and put a few inches of gravel in the bottom of each hole so the end of a wood post isn't sitting in water.
  • Use posts rated for ground contact. Ordinary treated lumber for above-ground use rots out at the base within a few years.
  • Gate posts carry the most load. Many builders use a size up (6 × 6 or 125 mm) for the hinge post, or set it deeper.
  • Check property lines, height limits and permit rules before you dig, and call 811 (or your local utility locating service) a few days ahead.

Frequently asked questions

How many fence posts do I need for 100 feet?

For a straight 100 ft run with no gates, posts at 8 ft spacing give 13 bays and 14 posts. At 6 ft spacing it is 17 bays and 18 posts. Add one post for every corner and one for every gate.

How many pickets do I need for a 100 ft privacy fence?

With 1 × 6 pickets (5½″ actual width) butted tight, 100 ft takes 219 pickets. With 10% extra for splits and cuts, buy 241. A 1 × 4 picket fence with 2½″ gaps needs far fewer, about 200 pickets per 100 ft before waste.

How many bags of concrete per fence post?

A 4 × 4 post set 2 ft deep in a 10″ hole needs about 0.92 cu ft of concrete: roughly 2.5 bags of 50 lb fast-setting mix or 1.5 bags of 80 lb concrete mix. In metric, a 100 mm post 600 mm deep in a 300 mm hole takes about 0.036 m³, or 3.3 bags of 20 kg post mix.

How deep should fence posts be?

The common rule is about a third of the post's height above ground, and at least 2 ft (600 mm). A 6 ft fence therefore needs 2 ft of post in the ground and 8 ft posts; a 1.8 m fence needs 2.4 m posts. In cold climates, set posts below the frost line so they don't heave.

How far apart should fence posts be?

For wood fences built on site, 6–8 ft (1.8–2.4 m) center to center. Go closer in windy areas or for tall, solid fences. For prefab panels, the spacing is the panel width plus one post, for example 99.5″ for 8 ft panels on 4 × 4 posts.

How many rails does a fence need?

Two rails per bay for fences up to 4 ft (1.2 m) high, three rails for fences up to 6 ft (1.8 m) and four for anything taller. The extra rails stop tall pickets from warping and bowing.

How many fence panels do I need for 30 meters?

With 6 ft (1.83 m) panels on 100 mm posts, each bay is 1.93 m, so a straight 30 m run takes 16 panels and 17 posts. Each corner or gate adds a post, and you may need to cut the last panel to fit.

These results are estimates for planning and budgeting. Actual quantities depend on site conditions, products and workmanship. Check structural and code requirements with a licensed professional before you build.