Fence Calculator
Estimate the posts, rails, and pickets a fence needs from its length, post spacing, and picket width, with concrete bags for setting the posts.
Cómo usar esta calculadora
- 1Enter the total length of the fence run.
- 2Set the post spacing — closer spacing is sturdier but uses more posts.
- 3Choose the rails per section and the picket width and gap.
- 4Read the posts, rails, and pickets to order, plus corner posts and concrete.
Cómo funciona
Fence materials
sections = ⌈length ÷ post spacing⌉ line posts = sections + 1 (plus corners and gates) rails = sections × rails per section pickets = ⌈length ÷ (picket width + gap)⌉
A fence estimate is a chain of simple counts. First divide the run by the post spacing and round up to get the number of sections (the bays between posts). The number of line posts is one more than the number of sections, because a fence with, say, twelve bays has posts at both ends and between each bay — the classic 'fencepost' counting that trips people up. Rails multiply the section count by however many horizontal rails each bay uses, from two on a low fence to four on a tall or heavy one. Pickets, if the fence has them, come from dividing the total length by the combined width of one picket plus its gap. Corner and gate posts are added on top, and post-setting concrete is estimated per post.
Ejemplo resuelto
A 100 ft fence with posts every 8 ft needs ⌈100 ÷ 8⌉ = 13 sections, so 14 line posts (plus corners). With three rails per section that is 39 rails, and 5.5-inch pickets set tight give ⌈1,200 ÷ 5.5⌉ ≈ 219 pickets — the classic off-by-one being that 13 gaps need 14 posts.
Fence Calculator: la guía completa
The fencepost problem, in the flesh
The single most common fencing mistake is under-ordering posts by one. It is a real-world instance of the classic 'fencepost problem' in counting: a straight fence divided into n sections has n + 1 posts, because a post is needed at both ends as well as between every pair of sections. Ten sections need eleven posts, not ten. Forget the extra end post and you arrive at the last bay one post short, mid-installation.
Corners and gates add still more. Every change of direction needs its own post, and a gate typically needs two sturdy posts to hang from and latch against. These do not follow the simple spacing math, so they are counted separately and added on. This calculator asks for the number of corner and end posts precisely because they sit outside the sections-plus-one rule, and leaving them out is the quiet way an order comes up short.
Choosing post spacing and rail count
Post spacing is a trade-off between cost and strength. Wider spacing uses fewer posts and less concrete, saving money, but longer unsupported rails sag more and the fence is weaker in wind. For most residential fences, 6 to 8 feet between posts is the sweet spot. Exposed, windy sites, heavy solid panels, or tall privacy fences argue for the closer end of that range or even tighter, since wind load rises steeply with height.
The number of rails should match the fence's height and weight. A low fence up to about 5 feet is fine with two rails, top and bottom. A standard 6-foot fence usually wants three, adding a middle rail to stop the pickets bowing. Taller fences or heavy boards benefit from four. More rails mean a stiffer, longer-lasting fence at modest extra cost, so when in doubt it is usually worth adding one rather than skimping.
Setting posts and estimating concrete
The posts are what hold a fence up, and how they are set matters more than almost anything else. A widely used rule is to bury at least a third of the post's above-ground height — so a 6-foot fence wants posts set about 2 feet deep, in a hole roughly three times the post's width. Below the frost line in cold climates, or the fence can heave when the ground freezes. Deeper and wider holes make a stronger fence but use more concrete.
The concrete estimate here assumes about one and a half 50-pound bags of mixed concrete per post, which suits a typical 4×4 post in a 2-foot hole. Larger posts, deeper holes, or gate posts that carry more load will use more; a light rail fence in firm ground may use less. Because setting posts is the hardest part to redo, it is worth erring toward deeper holes and a bag or two of spare concrete rather than discovering a wobbly post after everything has cured.
Preguntas frecuentes
How many fence posts do I need?
Divide the fence length by the post spacing and round up to get the number of sections, then add one — a straight run always needs one more post than sections, because both ends need a post. Then add extra posts for every corner and gate, which sit outside that rule.
How far apart should fence posts be?
For most residential fences, 6 to 8 feet between posts balances strength and cost. Use closer spacing for tall privacy fences, heavy panels, or windy, exposed sites, where longer spans would sag or catch too much wind. Wider spacing saves posts but weakens the fence.
How deep should fence posts be set?
Bury at least a third of the post's above-ground height — about 2 feet for a 6-foot fence — in a hole roughly three times the post's width, and below the frost line in cold climates. Deeper, wider holes make a sturdier fence but use more concrete.
How much concrete per fence post?
Roughly one and a half 50-pound bags of mixed concrete per post for a typical 4×4 post in a 2-foot hole. Larger posts, deeper holes, and gate posts need more. It is worth having a spare bag or two, since a poorly set post is hard to fix later.