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Fence Calculator

Posts, post holes, concrete, rails and pickets for a wood privacy or picket fence.

Fence
Add up every side you are fencing.
Posts
Posts
6 to 8 ft is common for wood fences. Match the length of your rails or panels.
A 4 × 4 post is about 3.5 in wide; a 6 × 6 is about 5.5 in.
Boards
Boards
Many builders use 2 rails for fences up to about 4 ft and 3 for taller fences.
0 for a privacy fence; 2 to 3 in for a classic picket fence.
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Your prices
Your prices
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Posts 14 posts 14 posts at least 9 ft long, each in a 10.5 in wide hole 42 in deep.

Posts and holes

Post length, at least
9 ft
Hole depth (with 6 in gravel)
42 in
Hole diameter
10.5 in

Concrete and gravel

80 lb concrete bags
33 bags
Or 50 lb bags
53 bags
Concrete
19.6 cu ft
Gravel for hole bottoms (0.5 cu ft bags)
9 bags

Boards

Rails
39 rails
Pickets
230 pickets

Cost

How many fence posts do I need?

Divide the fence length by the post spacing, round up, and add one post to finish the line, plus one for each corner and each gate. A 100 ft fence with posts every 8 ft needs 14 posts. For a 6 ft fence each post should be at least 9 ft long, set in a 10.5 in wide hole 42 in deep, which takes about 33 bags of 80 lb concrete in total.

Worked example: a 100 ft privacy fence, 6 ft high

  1. Posts: 100 ÷ 8 = 12.5, round up to 13, plus 1 to finish = 14 posts.
  2. Post length: a third of the post goes in the ground, so a 6 ft fence needs posts at least 6 × 1.5 = 9 ft long, 3 ft of it buried.
  3. Holes: about 3 times the post width (3.5 in × 3 = 10.5 in) and 3 ft deep plus 6 in for gravel = 42 in.
  4. Concrete: fill each hole to about 3.5 in below the top. That's about 1.4 cu ft per post, 19.6 cu ft in all: 33 bags of 80 lb (or 53 of 50 lb).
  5. Rails and pickets: 13 sections × 3 rails = 39 rails. 1,200 in ÷ 5.5 in pickets, plus 5% = 230 pickets.

Posts and pickets per 100 ft of fence

Straight fence, no corners or gates, 5.5 in pickets with no gap, 5% extra pickets.

Post spacingPostsSectionsPickets
6 ft1817230
7 ft1615230
8 ft1413230

Picket count depends on the fence length and picket width, not the post spacing.

Setting posts in concrete

  • Hole width: about 3 times the width of the post (Quikrete).
  • Hole depth: one third of the post's overall length, plus 6 in for a gravel base that drains water away from the post. Go deeper where the ground freezes: structural posts should sit at least 6 in below the frost line.
  • Concrete: fill to about 3 to 4 inches from the top, then slope the top away from the post so water runs off.
  • Gates and corners take the most strain. Consider larger posts or deeper holes there.

Before you dig

  • Call 811 a few days ahead to have underground utilities marked. It's free.
  • Check your property line and any HOA or town rules on height and style.
  • Match the spacing to your rails or panels. 8 ft rails need posts 8 ft apart, center to center.
  • Buy posts by stock length: if the calculator says 9 ft, buy 10 ft posts and cut the tops level after setting.

Frequently asked questions

How many bags of concrete per fence post?
For a 4 × 4 post on a 6 ft fence, in a 10.5 in wide hole with 3 ft buried, about 1.4 cu ft: roughly 2.3 bags of 80 lb, or 3.7 bags of 50 lb. Over a whole fence, round up the total, not each hole.
How deep should fence posts be?
One third of the post's overall length, plus 6 in of gravel underneath (Quikrete). For a 6 ft fence that means 9 ft posts, buried 3 ft, in a 3.5 ft deep hole. In cold climates, go below the frost line.
How far apart should fence posts be?
6 to 8 ft is typical for wood fences. Match the spacing to your rail or panel length; more than 8 ft lets rails sag.
How many pickets do I need for 100 ft of fence?
For 5.5 in pickets with no gap: 1,200 in ÷ 5.5 = 219, or about 230 with 5% extra. With a 2.5 in gap between 3.5 in pickets: 200, or 210 with extra.
How wide should a post hole be?
About 3 times the post width: roughly 10 to 11 in for a 4 × 4 post (3.5 in actual) and about 16.5 in for a 6 × 6 (5.5 in actual).

Guides

Related calculators

Board Foot CalculatorBoard feet and cost for any stack of lumber, hardwood or softwood.Concrete CalculatorCubic yards and 40, 60 or 80 lb bags for slabs, footings, posts and steps.Deck CalculatorDeck boards, joists and screws or hidden fasteners for any deck size.Gravel CalculatorTons, cubic yards and bags of gravel for a driveway, path or patio.

Sources and method

Last checked October 12, 2026. How we build and test every calculator: methodology.